Foreign Secretary Boris Johnson is holding a series of top-level talks in a bid to show the UK's international standing has not been damaged by Brexit.
Mr Johnson is meeting US secretary of state John Kerry in a get-together which London hopes will demonstrate that Washington still values the "special relationship" between the two countries after the surprise vote to withdraw from the EU.
After that engagement, Mr Johnson is hosting talks on Syria with his counterparts from the US, Germany, France and Italy, along with the EU foreign affairs chief Federica Mogherini.
Following that gathering, Mr Johnson is attending a meeting with foreign ministers from Saudi Arabia and the UAE to discuss the conflict in Yemen.
Speaking ahead of the meetings, Mr Johnson said: "We must be more active, more engaged and more outward-looking, so I am delighted to have this early opportunity to welcome my international counterparts to London for important meetings on the conflicts in Syria and Yemen.
"I will be making clear my view that the suffering of the Syrian people will not end while Assad remains in power. The international community, including Russia, must be united on this."
Mr Johnson will travel to Washington DC on Thursday for talks on combating Islamic State.