President Joe Biden urged Republicans on Wednesday to drop opposition to a long-delayed military aid package for Ukraine and Israel, saying the US allies are in a "pivotal" moment of conflicts against Russia and Iran.

"While both countries can capably defend their own sovereignty, they depend on American assistance, including weaponry, to do it. And this is a pivotal moment," Biden wrote in an op-ed in The Wall Street Journal.

Biden's direct appeal came as Republicans in the House of Representatives continue to squabble over whether to back Ukraine, which is running out of ammunition as it fights for a third year against President Vladimir Putin's invasion.

Billions of dollars of aid -- already approved in the Senate, before being blocked in the House -- would also renew the US weapons flow to Israel which came under a massive drone attack by Iran over the weekend.

"It's a strong and sensible plan. It shouldn't be held hostage any longer by a small group of extreme Republican House members," Biden wrote.

Republican House Speaker Mike Johnson has said he will introduce his own aid plan shortly, but he faces a fierce backlash from hard-right members of his party who oppose further military support for Ukraine and it remained unclear Wednesday when or whether the speaker would be able to move ahead.

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Biden argued in the Journal that the aid is needed for US security.

"Both Ukraine and Israel are under attack by brazen adversaries that seek their annihilation. Mr Putin wants to subjugate the people of Ukraine and absorb their nation into a new Russian empire. The government of Iran wants to destroy Israel forever -- wiping the world's only Jewish state off the map," Biden wrote.

"America must never accept either outcome -- not only because we stand up for our friends, but because our security is on the line, too."

In an attempt to address Republican criticism that the United States cannot afford to spend money on Ukraine's fight against Russia, Biden said it would not be "blank checks."

The weaponry for Ukraine would be built in US factories, he said.

"We'd be investing in America's industrial base, buying American products made by American workers, supporting jobs in nearly 40 states, and strengthening our own national security. We'd help our friends while helping ourselves," Biden said.

He also sought to allay concerns about the aid to Israel within his own Democratic party, where growing numbers of members oppose arming Israel during its devastating war against Hamas in civilian-packed Gaza.

The bill approved by the Senate, Biden said, includes funding to "continue delivering urgent humanitarian aid for the people of Gaza."