America's new Secretary of State John Kerry will hold talks with the Prime Minister and Foreign Secretary William Hague on the first stop in an 11-day world tour.
The conflict in Syria, nuclear stand-off with Iran and Middle East peace process are expected to be high on the agenda.
But the Falklands is also likely to come up - with Washington under pressure to recognise the result of a referendum next month on whether the islanders want to remain British.
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Donald Trump's press secretary will hold his first full briefing today after a weekend in which the administration clashed with the media.
All weekend it felt as though the new administration had a self-destruct button and was desperately searching for it.
Areas of dense freezing fog across the south-east could cause flight delays until at least 10.30am, according to forecasts.