Ukraine’s president, Volodymyr Zelenskiy, has urged the US to stay united in its support amid worries about the consequences of a Republican win in Tuesday’s midterm elections.

If the US Democrats lose control of the House of Representatives and the Senate, the colossal financial and military support provided to Ukraine under the Democrats could falter.

Ahead of Tuesday’s results, Zelenskiy called for US politicians to maintain “unwavering unity” and follow Ukraine’s example “until peace is restored”.

“Democracies must not stop on their way to victory,” said Zelenskiy. “When Russia decided to destroy our freedom and wipe Ukraine off the face of the Earth, we immediately got united and we keep this unity.”

Most Republicans have supported helping Ukraine defend itself against Russia. In fact, Ukraine has been one of the few issues to garner strong cross-party support in recent years.

But in the lead-up to the midterm elections, prominent figures within the Republican party – particularly those in the Donald Trump wing – have put doubts over continuing to fund Ukraine.

Rightwing populist Republican Marjorie Taylor Greene told a Trump rally in Iowa last month that “not another penny will go to Ukraine” if the Republicans win as US interests should come first.

The House minority leader, Republican Kevin McCarthy, who could become the next speaker of the House, said that though Ukraine was important, there would be no “blank check” if the Republicans controlled Congress.

However, other Republicans have criticised the comments. Republican Adam Kinzinger said McCarthy was attempting to appease the far right of the party to be chosen as speaker.

Former vice-president Mike Pence has urged continued support, as has Michael Waltz, a member of the House Armed Services Committee, who emphasised that the majority of Republicans support aid to Ukraine as well as several key Republican senators, such as Mitch McConnell, the Republican leader in the Senate.

The US is by far Ukraine’s biggest financial backer. Since the invasion, the US has given Ukraine $18.9bn (£16.3bn) in aid and committed almost twice as much as Ukraine’s European allies.

Amid reports by the Washington Post that the US has asked Kyiv to signal it is open to negotiations in order to placate allies in parts of Europe, Africa and Latin America worried about a protracted war, Ukraine has doubled down on its terms for peace.

Ukraine has said it will only begin negotiations once Russia’s troops have left all of Ukraine, including Crimea and parts of eastern Ukraine that Russia occupied in 2014. Without this, presidential adviser Mykhailo Podolyak told Radio Svoboda on Tuesday, any deal would be a temporary truce that Russia would use to rearm and attempt to occupy Ukraine again.

Podolyak asserted in the interview that the Washington Post may be obtaining its information from pro-Russian politicians, describing the reports as part of “the information program of the Russian Federation”. He later went further, tweeting that the Kremlin was “hopelessly clinging” to the US midterm elections.

“They sincerely believe that Ukraine can surrender ‘at the call’ of the White House and are hopelessly clinging to the election,” tweeted Podolyak.

For the US, Podolyak said, it was “extremely beneficial” for Ukraine to win the war firstly because it would signal to other authoritarian leaders that if they attack another country, international law will be upheld, and secondly, because the US and its allies had invested too much to let Russia win.

“If Ukraine does not win the war … [then] despite the large and powerful financial, economic, military, and advisory assistance from Nato countries, above all the US, Russia won. You understand what will be proven in that case. That Russia’s military … is much better, Russia really has the ‘second army in the world’ [and] Russia can dictate conditions.”

In further comments to Italy’s la Repubblica, which reported that Ukraine’s allies envisaged negotiations beginning once Ukraine retakes its southern Kherson region, Podolyak said: “We have no choice … If we stop defending ourselves, we will cease to exist. Literally. Physically. We will continue to fight even if we are stabbed in the back.”

Ukraine’s allies, at least under the current framework, do not seem close to forcing Ukraine into negotiations with Russia – instead choosing to reiterate that it is Kyiv’s choice when and how negotiations take place.

The French president, Emmanuel Macron, said during a press conference at Cop27 that though the negotiations would need to happen at some point, “they should happen within the terms of who will be elected by Ukraine”.

US state department spokesperson Ned Price said during a briefing in Washington on Tuesday that Russia was doing the opposite of signalling it was ready for negotiations by “escalating the war”.

But the US did confirm it was keeping channels open with Russia to ebb global fears of nuclear war. Joe Biden’s national security adviser, Jake Sullivan, said it was in the interest of the US to talk to Russia, despite the war, adding that officials are “aware of who we are dealing with”.