The Pentagon is reviewing its weapons stockpiles and may need to boost military spending after seeing how quickly ammunition has been used during the war in Ukraine, the most senior US military official said.

General Mark Milley, chairman of the joint chiefs of staff, said the return of 20th-century ground warfare tactics in Europe was forcing US planners to reconsider assumptions made in recent decades that had led military strategists to retool capabilities for counter-terrorism and irregular combat in theatres such as Iraq and Afghanistan.

“One of the lessons of this war is the very high consumption rates of conventional munitions, and we are re-examining our own stockages and our own plans to make sure that we got it right,” Milley said in an interview with the Financial Times.

“We’re trying to do the analysis so that we can then estimate what we think the true requirement would be. And then we have to put that in the budget,” he added. “Ammunition is very expensive.”

Any review may result in an increase in the military’s $817bn annual budget. Milley’s comments come on the heels of a high-profile tour of allied capitals last week by Ukrainian president Volodymyr Zelenskyy, who made repeated requests for the west to increase its supply of armaments. Ukraine has received more than $29bn in either arms or defence spending from Washington since the conflict began.

The joint chiefs chairman was in Brussels on Tuesday, meeting other countries allied with Kyiv to co-ordinate massive amounts of lethal assistance ahead of a planned Ukrainian counter-offensive in the spring.

Milley’s remarks, which come a week before the first anniversary of Russia’s full-scale invasion of Ukraine, reflect a broader reckoning among western allies about the possibility of the war dragging on indefinitely.

The quantity of munitions required by the conflict has exposed vulnerabilities in the US defence industry, which is trying to pivot from peacetime production levels, and has also been beset by pandemic-related shortages in parts and labour.

Nato secretary-general Jens Stoltenberg warned on Monday that Ukraine was using ammunition at a rate “many times higher” than countries in the alliance could produce them, straining their defence industries.

Ukrainian forces are estimated to be firing more than 5,000 artillery rounds daily, while Russia is estimated to be consuming four times that amount as it pushes to take more territory in the east.

The increased urgency over ammunition supply comes as Kyiv is planning a major counter-offensive that will rely on billions of dollars’ worth of western weapons, including main battle tanks, infantry fighting vehicles and heavy artillery.

A recent report by the Center for Strategic and International Studies, a Washington think-tank, found that the US defence industrial base was “not adequately prepared” for the security environment and the munitions requirements of another major conflict such as a war with China in the Taiwan Strait was likely to exceed current Pentagon stockpiles.

However Mark Cancian, a senior adviser at CSIS’s international security programme, said he was confident the Pentagon was taking steps to address any readiness shortfalls and that its stockpiles were adequate for now.

“I’m moderately concerned but also optimistic that we are putting in place the fixes that we need,” he said.

Milley has been one of Washington’s most prominent advocates for a negotiated settlement between Kyiv and Moscow. While he did not tie the depletion of stockpiles to his support for peace talks, he said he still believed the war would end at the negotiating table, with neither side likely to achieve their military aims.

“It will be almost impossible for the Russians to achieve their political objectives by military means. It is unlikely that Russia is going to overrun Ukraine. It’s just not going to happen,” Milley said.

“It is also very, very difficult for Ukraine this year to kick the Russians out of every inch of Russian-occupied Ukraine,” he added. “It’s not to say that it can’t happen . . . But it’s extraordinarily difficult. And it would require essentially the collapse of the Russian military.”

When asked if the moment for diplomacy between Moscow and Kyiv had passed, Milley said: “We’re weeks away from the beginning of spring, but it’s a rolling window. There’s opportunities at any moment in time.”

However, he said, both sides were “dug in pretty hard on their objectives” and unwilling to negotiate.

Milley said the conflict echoed a lesson from the second world war that aggression must be stopped “with firmness, deterrence, military power”, though he noted that with Russia’s nuclear arsenal the stakes were now higher.

“In this particular case, it’s against a country that is large and is nuclear-armed,” he said. “So you have to be very, very conscious about managing escalation. At the same time, you have to uphold the principles for which the United Nations was founded and which the international order is resting on.”