The US authorities have invited Ukrainian President Vladimir Zelensky to address senators via video link at a classified briefing on Tuesday regarding the allocation of funds for additional aid to Kiev, US Senate Majority Leader Chuck Schumer said.

"We can hear directly from him precisely what's at stake in this vote," Schumer said. "I ask that all senators - all senators - attend this important briefing."

Head of the US Office of Management and Budget Shalanda Young sent a letter to American legislators on Monday warning that the United States would run completely out of funds to support Ukraine by the end of the calendar year, unless Congressmen approved a package that the White House had been seeking. "We are out of money - and nearly out of time," she stated.