Palm Beach, Florida - Donald Trump met with the UK's Foreign Secretary David Cameron on Monday at Mar-a-Lago, British officials said, in a move described as "unusual."

"Ahead of his visit to Washington, the Foreign Secretary met former president Trump in Florida," said a UK Foreign Office spokesman on Tuesday.

"It is standard practice for ministers to meet with opposition candidates as part of their routine international engagement," he added.

The Guardian's politics editor, Pippa Crerar, disputed that characterization, calling the meeting an "unusual situation."

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Cameron is due in Washington for discussions on Tuesday with Secretary of State Antony Blinken.

While British officials were not drawn on the substance of the Trump talks, the Foreign Office said Cameron would push, in his meeting with Blinken, for a "full, urgent, and transparent investigation" into Israeli air strikes that killed seven aid workers in Gaza last week.

Like the US, the UK government has faced calls to suspend arms exports to Israel after three Britons working for US-based food charity World Central Kitchen were killed in the attack.

More than 600 lawyers, including former Supreme Court judges, warned in a letter that London risked breaching international law by continuing to allow the export of weapons to Israel.

Cameron is also expected to urge congressional leaders to approve a proposed $60-billion military aid package for Ukraine that Republicans have been blocking for months.

Ukrainian President Volodymyr Zelensky warned on Sunday that Ukraine will lose its war with Russia if Congress does not approve the stalled package.