Pete Hegseth, the US defence secretary, has said it is “unrealistic” to expect Ukraine to return to its pre-2014 borders, when Russia first took control of Crimea.

Speaking at a meeting of the Ukraine Defence Contact Group in Brussels, Hegseth said it would only be possible to establish a “durable peace” with a “realistic assessment of the battlefield”.

The US defence secretary also downplayed suggestions of Ukraine joining Nato and ruled out deploying US troops to Ukraine under any future security arrangements.

Kyiv has repeatedly called for Nato membership and has in the past rejected ceding territory as part of a peace deal.

Hegseth, who was appointed defence secretary after Donald Trump returned to the US presidency in January, told the meeting of more than 40 countries allied to Ukraine: “We want, like you, a sovereign and prosperous Ukraine.

“But we must start by recognising that returning to Ukraine’s pre-2014 borders is an unrealistic objective.

“Chasing this illusionary goal will only prolong the war and cause more suffering.”

Russia annexed the Black Sea peninsula of Crimea from Ukraine in March 2014 and then backed pro-Russian separatists in an armed insurgency against Kyiv’s forces in eastern Ukraine.

Moscow currently controls around a fifth of Ukraine’s territory, mainly in the east and south.

Hegseth said any durable peace must include “robust security guarantees to ensure that the war will not begin again”.

However, he said “the United States does not believe that Nato membership for Ukraine is a realistic outcome of a negotiated settlement”.

Instead, security guarantees should be backed by “capable European and non-European troops”.

“If these troops are deployed as peacekeepers to Ukraine at any point, they should be deployed as part of a non-Nato mission and they should not be covered under Article 5,” he said, referring to the alliance’s mutual defence clause.

Trump has consistently said his priority is to end the war, which began with Russia’s full-scale invasion of Ukraine in February 2022. He has also been critical of US spending on military aid for Kyiv.

Earlier this week, Ukrainian President Volodymyr Zelensky said he was ready to negotiate a peace deal with Russia but wanted his country to do so from a “position of strength”.

Speaking to the Guardian, Zelensky said if Trump was able to get Ukraine and Russia to the negotiating table, the Ukrainian president planned to offer Russia a straight territory exchange, giving up land Kyiv has held in Russia’s Kursk region since the launch of a surprise offensive six months ago.

“We will swap one territory for another,” he said, but added that he did not know which part of Russian-occupied land Ukraine would ask for in return.

“I don’t know, we will see. But all our territories are important, there is no priority,” he said.

He also said he would offer US firms lucrative contracts to rebuild Ukraine, in an apparent attempt to get Trump onside.