The United States wants Ukraine and Russia to end their nearly four-year war by June, and has offered to host talks between the two sides in Florida next week, Ukrainian President Volodymyr Zelenskyy said.
US-led efforts to end Europe's deadliest conflict since World War II have stepped up a gear in recent weeks, but Moscow and Kyiv remain at odds over the key issue of territory.
Russia, which occupies around 20 percent of its neighbour, is pushing for full control of Ukraine's eastern Donetsk region as part of any deal and has threatened to take it by force if talks fail.
But Ukraine says ceding ground will embolden Moscow and has signalled it will not sign an agreement that fails to deter Russia from invading again.
"The United States has proposed for the first time that the two negotiating teams — Ukraine and Russia — meet in the United States, probably in Miami, in a week's time," Zelenskyy told reporters.
"They say that they want to do everything by June," he added.
The US has mediated two rounds of negotiation between the two sides in Abu Dhabi since January, brokering a major prisoner exchange but failing to reach a breakthrough on territory.
Both Moscow and Kyiv say talks have been difficult.
'Free economic zone'
Zelenskyy has repeatedly expressed frustration that his country is being asked to make disproportionate compromises compared to Russia.
Ukraine has proposed freezing the conflict along the current front lines.
But Russia has rejected this, and Washington has pushed for Kyiv to convert the land it currently controls in the Donetsk region into a "free economic zone" where neither side has military control.
"Even if we come to the creation of a free economic zone, we will need fair and reliable rules," Zelenskyy said.
The two sides have also failed to reach a "common understanding" on the issue of control over the Russian-occupied Zaporizhzhia nuclear power plant, Zelenskyy said.
Russian forces seized the plant, the largest in Europe, at the start of the conflict and have held onto it since.
Ukraine will not tolerate Russia and the United States making deals about Ukraine behind its back, Zelenskyy added.
Russia hits Ukraine's grid
Throughout the negotiating progress Russia has launched waves of deadly strikes on Ukraine that have cut heating and power to millions during freezing temperatures.
Russian attacks earlier Saturday forced Ukraine's three operating nuclear power plants to throttle their generation capacity, "creating a direct risk of a nuclear incident", foreign minister Andriy Sybiga said.
The UN's atomic energy watchdog issued a statement calling for "restraint".
Russia, which denies targeting civilians, accused Ukraine on Friday of orchestrating the shooting of a top military intelligence general in Moscow, leaving him wounded. Kyiv has yet to comment.
Russia invaded Ukraine in February 2022, describing it as a "special military operation" to prevent the expansion of NATO, a war aim that Kyiv has called a pretext for an illegal land grab.
The conflict has resulted in a massive wave of destruction that has left entire cities in ruins and killed tens of thousands of soldiers and civilians, while forcing millions to flee their homes.
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