WASHINGTON - Ukraine President Volodomyr Zelensky and top aides to US President Joe Biden will make their case to US senators on Dec 6 about why a fresh infusion of military assistance is needed to help Ukraine repel Russian invaders.

US officials say the United States will spend all it has available for Ukraine by the end of the year, a dire prediction that comes as Kyiv has struggled to make major advances in its 2023 counteroffensive against Russia.

Mr Biden's administration in October asked Congress for nearly US$106 billion (S$140 billion) to pay for ambitious plans for Ukraine, Israel and US border security, but Republicans who control the House with a slim majority rejected the package.

Senate Majority Leader Chuck Schumer, a close Biden ally, announced on Dec 4 night that the administration has invited Mr Zelensky to address senators via secure video as part of a classified briefing on Dec 5 "so we can hear directly from him precisely what's at stake in this vote."

In addition, a variety of top Biden officials, including Defence Secretary Lloyd Austin and Secretary of State Antony Blinken, are expected to brief the senators on Dec 5.

Mr Schumer also started the process of advancing a Ukraine-Israel emergency aid Bill on the Senate floor.

"America's national security is on the line around the world" with the fate of Ukraine aid hanging in the balance, Mr Schumer said in a Senate speech.

"Autocrats, dictators waging war against democracy, against our values, against our way of life. That's why passing this supplemental is so important. It could determine the trajectory of democracy for years to come."

Mr Zelensky told Reuters in a November interview that despite the slow going, Ukraine would try to deliver battlefield results by the end of the year and that he remained sure Kyiv would eventually have success in the war despite difficulties at the front.

But the stalled drive to get US assistance has alarmed the Biden White House, which fears a failure to help Ukraine further would increase the likelihood of Russian victories. REUTERS