Ukraine formally started the screening process to begin talks over its future membership of the European Union on Thursday, President Volodymyr Zelenskyy said.

In a post on X, the Ukrainian leader said he welcomed the start of “substantial preparations for Ukraine’s EU accession talks” in Brussels, following an agreement reached with EU Commission President Ursula von der Leyen last week at the World Economic Forum in Davos, Switzerland.

“The thorough work of assessing the conformity of Ukrainian legislation with EU norms, the formation of Ukraine’s delegation, and our negotiating position are all ahead of us,” Zelenskyy added.

“I expect full engagement of Ukrainian government team and the first intergovernmental conference to be held already this spring.”

Across the Atlantic, bipartisan U.S. Senate negotiations over a border security deal that ties in aid for Ukraine have hit a critical juncture, Republican Senator John Thune told reporters on Thursday, according to Reuters. The White House said last week that the U.S. money supply to Ukraine has now run out, which could leave Kyiv ill-equipped to repel the Russian invasion.

A small bipartisan group of senators is seeking a way to please Republicans aligned with Donald Trump, the front-runner for the party’s presidential candidacy, who has openly pressured allies not to compromise on legislation that would help President Joe Biden in the run-up to November’s election.

Meanwhile, Moscow and Kyiv continue to trade allegations over the shooting down on Wednesday of a Russian military transport plane that was carrying 65 Ukrainian prisoners of war and nine Russians.

Russia blamed Ukraine for the plane crash, saying it had used Western missiles to shoot the military transport Ilyushin-76 plane down over the border region of Belgorod, killing all on board, while the aircraft was en route to a prisoner exchange.

A senior Russian lawmaker also alleged Ukrainian military intelligence had been given a 15-minute warning before the plane entered the area.

Ukraine has denied that it was given a warning, but has neither confirmed nor denied that its forces shot down the plane. Zelenskyy said Kyiv will fully investigate the circumstances around the crash, adding that “facts” were a key priority. He accused Russia of “playing with the lives of Ukrainian prisoners, with the feelings of their relatives and with the emotions of our society.”