The White House has said that the US presidential administration does not have a "plan B" if Congress continues to block aid for Ukraine, and so hopes to eventually secure additional funding from US lawmakers.

"At the end of the day, there is no alternative to the United States stepping up to the plate and providing a level of resources that allow Ukraine to have the artillery, the air defence systems and the other capabilities they need," US National Security Advisor Jake Sullivan said during a press conference.

He said he remains hopeful that the aid for Ukraine will be passed, adding that "a significant number of Republicans" have recently acknowledged the need to "move forward a package of support for Ukraine".

"And time is of the essence in this regard. So we're going to stay focused on that and we believe that we still can and will deliver it," Sullivan said.

The US Senate will once again consider a separate bill on aid for Ukraine, Israel and Taiwan, which will not include the immigration reform that divides Democrats and Republicans, on 8 February.

The US Senate did not receive enough votes for a procedural vote on a bill to strengthen migration policy, which included additional funds for Ukraine, Israel and Taiwan.

On 4 February, the US Senate introduced a US$118 billion bipartisan border security bill, which includes US$60 billion aid for Ukraine and US$14 billion for Israel.

US President Joe Biden in turn called for the bill to be passed as soon as possible.