BRUSSELS, Belgium–The US decision to step up military support for Israel after the surprise assault by Hamas will not harm Washington's ability to keep arming Ukraine, its NATO envoy said on Tuesday.

"On the question of whether or not US support for Israel could possibly come at the expense of US support for Ukraine -- we don't anticipate any major challenges in that regard," US ambassador Julianne Smith told journalists.

"I suspect the United States will be able to stay focused on our partnership and commitment to Israel's security while also meeting our commitments and promise to continue supporting Ukraine."

President Joe Biden ordered US ships and warplanes to move closer to Israel in a show of support on Sunday, while also sending fresh military aid.

The crisis in Israel comes as the White House is scrambling to find a way to keep weapon supplies flowing to Ukraine after turmoil in the US Congress.

Kyiv's international backers are meeting in Brussels on Wednesday to discuss arms deliveries, with a focus on keeping Ukraine's counter-offensive advancing and providing air defences to protect against a suspected winter onslaught by Russia.

"I anticipate that the emphasis will be mostly on air defence and ammunition, although no doubt the Ukrainians will come in with a variety of other requests," Smith said.

Biden has sought to calm nerves among allies over Washington's backing for Kyiv after new assistance was dropped from a deal in the US Congress to avoid a government shutdown this month.

The US has given as much military support to Ukraine on its own as all European NATO members and Canada combined since Moscow launched its all-out invasion last year.

Western diplomats at NATO insist there is no danger of arms supplies to Ukraine drying up in the near future.

But the European Union's top diplomat has warned the bloc would not be unable to fill any funding gap left by the United States.