Iranian state television cited informed sources as saying Britain was directly involved in Sunday's suicide attack on the elite Revolutionary Guards, which killed several senior officers, Reuters reported.
The Guards had earlier blamed "foreign elements" linked to the United States for the attack in the southeastern province of Sistan-Baluchestan.
The attack and the allegations of foreign involvement are likely to raise tension between Iran and the West, a day before nuclear talks in Vienna including Iranian, U.S., French and Russian officials.
"Some informed sources said the British government was directly involved in the terrorist attack ... by organizing, supplying equipment and employing professional terrorists," state television said.
The television report said analysts believed the aim of the attack was to "re-direct" parts of the West's problems in Afghanistan across the border to Iran.
A Foreign Office spokesman in London declined to comment directly on the Iranian comments and instead issued a statement, saying: "The British government condemns the terrorist attack in the province of Sistan and Baluchestan in Iran and the sad loss of life which it caused.
"Terrorism is abhorrent wherever it occurs. Our sympathies go to those who have been killed in the attack and to their families," it said.