Prime Minister Andy Burnham of Britain said Wednesday that his government believes Iran “played a part” in the incident on Sunday at an air base used by American bombers in the U.S.-Israeli war against Iran.

“There are strong indications that Iran played a part in what happened over the weekend at R.A.F. Fairford,” Mr. Burnham told the BBC, referring to the British base about 90 miles outside of London. He added, “It remains an ongoing, complex and serious police investigation, and of course we are working closely with our colleagues in the United States of America.”

The arrest of five men early Sunday morning near the base on suspicion of explosives violations and terrorism triggered more than two days of anxiety as the police and military used a bomb disposal robot to examine three white vans and evacuated more than 85 nearby homes. The five men, who are British citizens, were released on bail on Monday. The authorities said on Tuesday that they had found no explosives in the vans, only an unspecified quantity of gasoline.

The Iranian Embassy in Britain on Monday issued a statement rejecting any suggestion that its government was involved. Mr. Burnham refused to say why the government believes Iran was connected, saying, “We will say more in due course.”