Ukrainian President Volodymyr Zelenskyy said the United States has set a June deadline for Ukraine and Russia to reach an agreement to end the nearly four-year war.
U.S.-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 so 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 in comments made public early Saturday.
"They say that they want to do everything by June," he added.
The U.S. has mediated two rounds of negotiations 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 said talks have been difficult.
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.
Russia has rejected this and Washington has instead 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, Zelensky 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.
Throughout the negotiating progress Russia has launched waves of deadly strikes on Ukraine that have cut heating and power to millions during freezing temperatures.
Kyiv says they are a war crime.
The country was forced to request emergency assistance from Poland on Saturday after Russia hit the Burshtynska and Dobrotvirska power plants in western Ukraine, causing blackouts across the country, Energy Minister Denys Shmygal said.
"Due to the damage caused by the enemy, emergency outages have been applied in most regions," grid operator Ukrenergo said on Saturday.
Ukraine's nuclear power plants were forced to "reduce their generation capacity", the energy ministry said.
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.
