The Speaker of the US House Mike Johnson has demanded that Ukraine fire its ambassador to Washington, as a feud between the Republican Party and Volodymyr Zelensky escalates.

Johnson's intervention comes after President Zelensky visited an arms factory in Scranton, Pennsylvania - the hometown of President Joe Biden in a key swing state - with several top Democrats.

In a public letter, the top Republican said the visit was "designed to help Democrats" and claimed it amounted to "election interference".

The row has threatened to overshadow Zelensky's meeting with President Joe Biden on Thursday, during which he will present a "plan for victory" in his country's war with Russia.

Since his arrival to the US on Sunday, Zelensky has ramped up efforts to persuade the US and other allies to lend more support to Ukraine as it fends off Russian advances.

On Thursday, Biden announced that the US will send $7.9bn (£5.9bn) worth of military aid to Ukraine in a surge of assistance as his presidency nears its end.

The aid, part of a $61bn package that passed Congress in April, includes additional Patriot air defence missiles and long-range munitions.

The weapons package will be approved through presidential drawdown authority and will pull from existing Pentagon supplies to deliver the arms more quickly.

Congressional Republicans blocked the Biden administration's $61bn military package for months earlier this year, before ultimately relenting and passing the legislation in April. Before that, arms supplies to Ukraine had dried up for several months.

The US has been the largest foreign donor to Ukraine, with $56bn provided for its defence to date.

In a statement ahead of his White House visit, Zelensky previewed three elements of his victory plan: further weapons donations, diplomatic efforts to force Russia to agree to peace, and holding Moscow accountable for its full-scale invasion in 2022.

Zelensky had planned to present his proposals to the two presidential candidates: Kamala Harris and Donald Trump.

However, an official on Donald Trump's campaign said the Republican nominee would not meet the Ukrainian leader on his tour of the US this week.

Trump and Zelensky have long held a fractious relationship. In 2019, Trump was impeached by the US House over accusations that he pressured Ukraine's leader to dig up damaging information on a political rival.

He has frequently echoed Russian talking points over the war. At a campaign event on Wednesday he mocked Zelensky as the "greatest salesman on Earth" and accused the Ukrainian leader of refusing to "make a deal" with Moscow.

During an earlier rally on Tuesday, Trump also praised Russia's military capabilities, saying: "They beat Hitler, they beat Napoleon - that’s what they do, they fight."

The former president's remarks come amid a growing row between Zelensky and the Republican party over his visit to an ammunition factory in Biden's hometown of Scranton in the key swing state of Pennsylvania.

During the visit, Zelensky appeared with Pennsylvania Governor Josh Shapiro and several other top Democrats. Speaker Johnson accused the president of taking part in a "partisan campaign event" designed to held Vice-President Kamala Harris' camapign.

Meanwhile, the Republican-led House Oversight Committee had already announced that it would investigate whether Zelensky's trip was an attempt to use a foreign leader to benefit Vice-President Kamala Harris' campaign.

Congressional Republicans blocked the Biden administration's $61bn military package for months earlier this year, before ultimately relenting and passing the legislation in April.

Before that, arms supplies to Ukraine had dried up for several months.

The US has been the largest foreign donor to Ukraine, with $56bn provided for its defence to date.