Foreign Secretary Lord Cameron has met former President Donald Trump in Florida, before heading onto Washington DC for talks.
The former PM is in the US for talks with senior government officials about the wars in Gaza and Ukraine.
It is not unusual for foreign secretaries to meet opposition candidates during visits abroad.
Lord Cameron has previously criticised Mr Trump, who will likely stand for the Republican Party in the US election.
During Lord Cameron’s visit to the US, he is expected to speak to US Secretary of State Anthony Blinken about support for Ukraine and bringing stability to the Middle East, the UK’s Foreign, Commonwealth and Development Office said.
Republican lawmakers have been blocking a proposed $60bn (£47bn) military aid package for Ukraine for months.
Mr Trump, and his supporters within the party, oppose the US package providing aid to Ukraine. Those in the House of Representatives have vowed to vote against the package without additional funding for US border security being agreed to first.
Lord Cameron has been urging Republicans for some time to approve the aid package, particularly angering Republican congresswoman and Trump loyalist Marjorie Taylor-Greene, who told the foreign secretary to “kiss my ass”.
She was responding to an article written by Lord Cameron, in which he warned the US against showing “the weakness displayed against Hitler in the 1930s”.
During his upcoming talks with Mr Blinken, Lord Cameron is also set to broach the deaths of three British men working for aid organisation World Central Kitchen in Gaza.
Last week, US media reported that Mr Blinken spoke with the father of the US-Canadian citizen who was also killed in the Israeli air strike.
In 2015, during his time as prime minister, Lord Cameron labelled Mr Trump’s proposed temporary ban on Muslims entering the US “divisive, stupid and wrong”.
“I think if he came to visit our country I think it’d unite us all against him,” Lord Cameron said at the time, when Mr Trump was not yet elected.
Mr Trump replied by warning he may not have a “very good relationship” with Mr Cameron during his presidency.
In his memoirs published in 2019, Lord Cameron further said that he found it “depressing” that Mr Trump could win an election, and that it was due to his “protectionist, xenophobic, misogynistic interventions”.