Brussels, Mar. 1: When Russia launched its invasion of Ukraine with nearly 200,000 troops, many observers — and seemingly President Vladimir Putin himself — expected that the force would roll right in and the fighting would be over quickly. Instead, after five days of war, what appears to be unfolding is a Russian miscalculation about tactics and about how hard the Ukrainians would fight.

No major cities have been taken after an initial Russian push toward Kyiv, the capital, stalled. While Russia appeared to pull its punches, Ukraine marshaled and armed civilians to cover more ground, and its military has attacked Russian convoys and supply lines, leaving video evidence of scorched Russian vehicles and dead soldiers.

But the war was already changing quickly Monday, and ultimately, it is likely to turn on just how far Russia is willing to go to subjugate Ukraine. The Russian track record in the Syrian civil war, and in its own ruthless efforts to crush separatism in the Russian region of Chechnya, suggest an increasingly brutal campaign ahead.

Signs of that appeared Monday in Ukraine’s second-largest city, Kharkiv, when Russia accelerated its bombardment of a residential district where heavy civilian casualties were reported, an attack that may have included cluster munitions, which are banned by many countries, but not Russia and Ukraine.

“We’re only in the opening days of this, and Putin has a lot of cards to play,” said Douglas Lute, a former U.S. lieutenant general and ambassador to NATO. “It’s too early to be triumphalist, and there are a lot of Russian capabilities not employed yet.”

Russian military doctrine toward taking cities is both grimly practical and deadly, favoring heavy artillery, missiles and bombs to terrify civilians and push them to flee, while killing defenders and destroying local infrastructure and communications before advancing on the ground.

“Russia has not yet massed its military capability in an efficient way,” Lute said. “But the Russian doctrine of mass firing and no holds barred was visible in Chechnya, and there is the potential that Russia will get its act together tactically, and that will result in mass fire against population centers.”

Russian forces advancing toward Kyiv continue to face “creative and effective” resistance, according to a senior Pentagon official who briefed reporters Monday. But Russia’s assault is in just the fifth day, and Russian commanders will likely learn from their failures and adapt, the official said, as Russian forces also did in Syria. U.S. officials say they fear that Russia may now escalate missile and aerial bombing of cities with major civilian casualties, the official said.

Many experts say that Putin appeared to miscalculate in assuming that a quick strike on Kyiv could dislodge the government of President Volodymyr Zelenskyy, and that Ukrainians would stay largely indifferent. That explains, the experts suggest, why Russia went in lightly, seemingly trying to limit civilian casualties.

But the Ukrainians surprised the Russians with their defense, and an early effort to seize a Kyiv airport with a spearhead group, to allow reinforcements to fly in, failed badly.

Russia has seemed markedly restrained in its use of force and even clumsy in the early days, said Mathieu Boulègue, an expert in Russian warfare at Chatham House. “They were paying the price of their own rhetoric, that this was a defensive war against fascists and neo-Nazis,” he said. But now “we have an irritated Kremlin, and we haven’t seen yet what Russia has in store.”

The world is “starting to see stage two, when they go in with heavy artillery and ground troops, as they are doing in Kharkiv and Mariupol,” he said.

“I’m afraid this is really the beginning,” Boulègue said. “We can see a follow-on invasion with more experienced troops, with more forces, fewer precision-guided systems, more attrition, more carpet bombing and more victims.’’

In their effort to take Kyiv quickly, based on “terribly flawed assumptions about Ukraine,” the Russians withheld much of their combat power and capabilities and “got a bloody nose in the early days of the war,” said Michael Kofman, director of Russia studies at CNA, a defense research institute.

“However, we are only at the beginning of this war, and much of the euphoric optimism about the way the first 96 hours have gone belies the situation on the ground and the reality that the worst may yet be to come,” he said.

Jack Watling, an expert in land warfare at the Royal United Services Institute, a defense research institution, returned from Ukraine 12 days ago and says he expects more pressure from Russian forces in the coming days. “The Russians have a lot of forces in Ukraine, and as they continue to advance in a steady pace, they can function in a combined way, and not as isolated tank columns, and they will apply a much higher level of firepower,” he said.

Analysts say they expect Russian forces to work to expand their hold on the pro-Russia, separatist enclaves of Donetsk and Luhansk in eastern Ukraine, and to capture a land bridge to Crimea in the south, while pushing troops down from the north to try to encircle the main Ukrainian army east of the Dnieper River. They are trying to surround Mariupol and take Kharkiv.

That encirclement would cut off the bulk of Ukraine’s forces from Kyiv and from easy resupply, the experts say, limiting the sustainability of organized resistance. Russian troops are also moving steadily toward Kyiv from three axes to try to surround it.

While Russian forces have had supply and logistical problems — in some cases stranding vehicles without fuel in the early days of the invasion — those of the Ukrainians are likely more severe. The Ukrainian army will start to run out of ammunition in a week, the experts suggest, and out of Stinger missiles and Javelin anti-tank missiles before then.

Countries belonging to NATO and the European Union are sending ammunition and Stinger and Javelin missiles into western Ukraine from Poland, a NATO member, through a still-open border. The European Union is even, for the first time, promising to reimburse member states up to 450 million euros for the purchase and supply of weapons and equipment like flak jackets and helmets to Ukraine.

But if the Russians cut off the cities, Watling said, it will be difficult to get those supplies to Ukrainian defenders. Russian helicopters are beginning to run interdiction flights near the Polish border, and more troops are likely to move down from Belarus to cut off supply routes from Poland, he said, especially if, as it seems likely, Belarusian troops enter the war.

Bad starts in previous conflicts did not keep Russia from prevailing, and often at a brutal cost.

In Syria, the Russians had early setbacks, bringing predictions of quagmire. Yet they adapted, using missiles, air power and artillery while their allies mostly went in on the ground. From 2015 to the end of 2017, Russian airstrikes were estimated to have killed at least 5,700 civilians, one-quarter of them children, according to the Syrian Observatory of Human Rights.

The two wars in Chechnya were especially brutal, destroying the capital, Grozny, and helping give Putin, then a new prime minister, a reputation for toughness. Many thousands died before Russia restored control and put a pro-Kremlin Chechen in charge.

To this point, Russia appears to have been restrained in Ukraine by the belief that “they could not turn Kyiv into Grozny and expect to govern the country,” Watling said. “But now we see the Kremlin approving demonstrative acts of extreme violence, starting in Kharkiv,” which has had severe shelling of civilian areas.

There have also been more shellings of Kyiv and Chernihiv, a city northeast of the capital.

“You don’t pacify a population that way and you lay the ground for insurgency,” Watling added.

That strategy also raises a question of morale, both among the Russian forces and the Russian public back home.

“A lot depends on how brutal the Russians are prepared to be,” said Ian Bond, foreign policy director for the Center for European Reform. “They can’t censor everything, so brutalizing Ukrainians for whom many Russians feel a connection may not be politically successful for Putin.”

At home, Putin is facing an increasingly difficult position, the experts suggest. “He has another roll of the dice in the military campaign,” said Malcolm Chalmers, the deputy director of the Royal United Services Institute research group in Britain. “But if he fails in week two as badly as in week one, he will be under pressure to find some way out of this.”

The miscalculation of the early days has been reinforced by the impact of unexpectedly severe and coordinated Western sanctions, which have already devalued the ruble and promise further economic turmoil for many ordinary Russians.

There have already been some prominent Russian voices criticizing the war, and some demonstrations in Russian cities. Repressing those will not keep the reality of the war away from most Russians.

“Putin has miscalculated and put his hand in a mangle,” Watling said. “The war will go on, but a lot will depend on the character of the resistance” — whether it means fighting in the cities or, as many expect, it reverts to a partisan war. “But the Ukrainians will not give up,” he said.

Curtis M. Scaparrotti, a retired four-star Army general and supreme allied commander in Europe, said that Ukrainian soldiers “can’t match the Russian units, but they won’t fold, either.”

The Ukrainians “have to survive and transition to an insurgency, a tough task to pull off,” he said in an email. “The Russians have to consolidate gains and control a big country with a hostile populace. Next few days will indicate how this may go. If it gets difficult, the Russians will get brutal.”-New York Times