Peace talks between the U.S. and Ukraine have stumbled over one main issue: how to force Ukraine to give up what the Kremlin has failed to seize during the war — the entirety of the Donbas region.

 “On the territory issue, Americans are simple: Russia demands Ukraine to give up territories, and Americans keep thinking how to make it happen,” a senior European official familiar with the negotiation process told POLITICO on condition of anonymity to discuss a sensitive matter.

 “The Americans insist that Ukraine must leave the Donbas … one way or another,” the official added.

Ukraine has insisted that any peace deal must involve the war being frozen on current lines. At present, some 30 percent of Donbas is still in Ukrainian hands.

“In general, the most realistic option is to stand where we stand. But the Russians are pressuring Kyiv to give up territories,” the European official said.

 And the U.S. keeps pushing Ukraine to agree to the deal quickly, with President Donald Trump once again getting visibly frustrated with Kyiv.

“Russia, I guess, would rather have the whole country when you think of it. But Russia is, I believe, fine with it [the U.S. plan], but I’m not sure Zelenskyy is fine with it. His people love it, but he hasn’t read it,” Trump said on the red carpet at the Kennedy Center awards in Washington on Sunday.

Zelenskyy has not commented on Trump’s latest remarks, but he told Bloomberg that the U.S. and Ukraine have not reached agreement when it comes to Ukraine’s east. Kyiv has been trying to explain to the U.S. that giving Vladimir Putin what he has not managed to win in more than three years of war will only encourage him to take more. It also feels pressured by the speed at which the Americans want to move.

“Maybe Trump also wants it to happen fast, so his team is forced to explain to him they are not the ones to blame for why this is not happening as fast as he wanted it to happen,” the European official said.

Last week, Putin said Russia will take Donbas anyway. However, Ukraine believes that giving up the remaining 30 percent of the Donetsk region, which includes the cities of Kramatorsk and Sloviansk, with a total population of more than 100,000, would allow Putin to invade the Dnipropetrovsk, Zaporizhzhia and Kharkiv regions, Zelenskyy said earlier this year.

In August, Zelenskyy said it would take Russia about four years to fully occupy Donbas.

“Therefore, it is important how America will behave, as a mediator or will it lean toward the Russians?” the European official said, adding that Ukraine is also waiting for clarity on what security guarantees the U.S. is ready to provide.