The top Republican in the US Senate called for the Biden administration to step up assistance for Ukraine, breaking with his counterpart in the House of Representatives who warned earlier this week that aid for Kyiv would be reined in should the GOP take control of the lower chamber.

“The Biden administration and our allies need to do more to supply the tools Ukraine needs to thwart Russian aggression,” Senate Republican leader Mitch McConnell said on Friday.

McConnell’s comments came several days after House minority leader Kevin McCarthy said he anticipates difficulty in passing additional aid for Ukraine if his party wins the House in November’s midterm elections — a result predicted by current polling.

By contrast, McConnell pledged that a Republican-controlled Senate would make additional aid to Ukraine a focus.

“A Republican majority in the Senate will focus its oversight on ensuring timely delivery of needed weapons and greater allied assistance to Ukraine,” he said.

Polls suggest the Senate is going to be finely balanced after the midterm elections. It could even maintain its 50-50 split, with the Democratic vice president Kamala Hlarris casting the decisive vote.

Aid for Ukraine must pass both chambers of Congress and then be signed by the president.

Congress has passed billions of dollars in assistance for Ukraine since the beginning of the war, most recently a $12.3bn package as part of a larger spending bill meant to avert a government shutdown.

The back and forth among leading Republicans highlight the divisions in the party over assistance for Ukraine. McCarthy said this week that Republicans won’t support “a blank cheque” for the country.

But others, such as McConnell and former vice-president Mike Pence, have said the US should not back away from supporting Kyiv.

“We must continue to provide Ukraine with the resources to defend themselves,” Pence said earlier this week during a speech at the conservative Heritage Foundation think-tank.