The Trump administration has stepped up pressure on Sir Keir Starmer after imposing sanctions on a Britain-based activist accused by U.S. intelligence of working on behalf of Hamas, according to reports.

The U.S. Treasury Department’s Office of Foreign Assets Control (OFAC) announced Jan. 21 that it was “taking action against Hamas’s covert links to nonprofit organizations.” 

The statement went on to name six Gaza-based groups and the Popular Conference for Palestinians Abroad (PCPA).

U.S. officials said the PCPA operates as a front for Hamas overseas. OFAC also designated Zaher Birawi, 64, accusing him of being a “senior official” in Hamas through his leadership role in the PCPA.

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The Treasury Department said Birawi is a founding member of the organization and part of its general secretariat, alleging the group was used to “clandestinely expand” Hamas’ international influence and fundraising.

This included backing flotillas that attempted to reach Gaza. Some have received public backing from prominent activists, including Greta Thunberg.

“Hamas continues to show a callous disregard for the welfare of the Palestinian people,” John K. Hurley, the U.S. Undersecretary for Terrorism and Financial Intelligence, said in a statement.

Hurley added that “the Trump administration will not look the other way while Hamas leadership and enablers exploit the financial system to fund terrorist operations.”

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The sanctions have put pressure on the U.K., which has been reviewing possible counterterror measures against Birawi for weeks, according to The Times.

U.K. Shadow Home Secretary Chris Philp said it was “good to see” the U.S. take action, adding, “Under no circumstances should Britain be a place of sanctuary for anyone involved in or supportive of terrorist (organizations) like Hamas.”

Alex Hearn of Labour Against Antisemitism said Birawi continued to broadcast from London and organize flotillas despite the U.S. designation.

Lord Austin of Dudley has urged the U.K. to examine the intelligence “very carefully.”

Birawi, who lives in Barnet in north London, has been in the U.K. for more than 30 years.

He chairs the Palestine Forum in Britain and is a prominent organizer of pro-Palestinian demonstrations in the city.

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He has been named in Parliament as a security concern, and Israel designated him a Hamas member in 2013, allegations he has consistently denied.

In 2023, Birawi said he is a “law-abiding British citizen” and rejected claims of links to Hamas, saying his work focuses on “defending the national and human rights of Palestinians who survive under occupation.”

Fox News Digital has reached out to Birawi and Sir Keir Starmer’s office for comment.