Several Republican senators walked out of a classified briefing on Ukraine Tuesday as it descended into a row over the border crisis, after President Volodymyr Zelenskyy unexpectedly canceled a videolink appearance to appeal for continued U.S. funding.

Zelenskyy had been due to update the senators on the latest developments in the conflict with Russia and press for them to support a procedural vote expected Wednesday on an emergency aid package that includes more than $60 billion for Kyiv.

The cash has been held up for weeks by a row in Congress, as the White House has warned that existing funds will run out by the end of the year and that Russia's President Vladimir Putin could win the war if lawmakers fail to act.