U.S. Secretary of State Rex Tillerson is due to arrive in London later on January 21 on the first leg of a weeklong trip to Europe that will also take him to Paris, Warsaw, and the World Economic Forum in Davos, Switzerland.
A U.S. official, speaking on condition of anonymity, has said that Iran would dominate Tillerson's meetings with U.S. allies.
The trip comes amid behind-the-scenes negotiations over the fate of the landmark agreement to curb Iran's nuclear program in exchange for easing crippling international sanctions targeting Tehran.
"As you know, we really emphasize close coordination with the British in particular and the French in our efforts to close the gaps in [the agreement] and in [the] next steps on how we curtail Iranian malign influence in the region," a State Department official told reporters on January 19. "So I think that'll be a very high priority in his conversations."
Earlier this month, U.S. President Donald Trump said that he wanted to work with European allies and Congress to fix what he called "disastrous flaws" in the 2015 Iran deal signed under his predecessor, Barack Obama.
Trump warned that Washington would withdraw from the deal if it is not strengthened within four months.
In London, Tillerson is set to meet with British Foreign Secretary Boris Johnson and national security adviser Mark Sedwill to discuss cooperation on Iran, Syria, Libya, North Korea, and Ukraine.
On January 23 in Paris, Tillerson will meet senior French officials on the same issues, then spend two days in Davos shadowing Trump at his first visit as president to the annual economic forum.
By January 26, he will be in Poland for more talks with senior officials on security and economic matters.
The U.S. official said that Tillerson will be discussing the U.S. military presence in Poland, which has hosted U.S. and other allied troops following Russia's 2014 seizure of Ukraine's Crimean Peninsula and its backing of armed separatists in eastern Ukraine.