Manouchehr Mottaki, the Iranian foreign minister, said on Wednesday that London's involvement was clear and that Tehran would make strong protests to Britain.
A little-known group campaigning for independence for Iran's Arab minority claimed responsibility in a web statement for Tuesday's attacks on a bank and government building in the oil city of Ahvaz.
"Yesterday's murders in Ahvaz were committed by those who proudly have their photographs taken with British officials," Mottaki said. "They enjoy the co-operation of British army commanders and use their facilities in Basra.
"We hope British officials take this seriously, put it on their agenda and act accountably."
A British foreign ministry spokesman rebuffed Mottaki's accusation. "We were not involved and condemn all terrorism," he said.
The claim of responsibility was posted on a website used by Iranian Arab fighters.
"Our heroes ... in the military wing of The Arab Struggle Movement for the Liberation of Ahvaz attacked and destroyed the dens of the occupying enemy," the statement said.
Ahvaz is situated in southwest
Iran, home to an Arab minority
Only about 3% of Iran's 69 million people are Arabs but authorities are very sensitive about protests and discontent in the southwestern Arab territories, home to Iran's biggest oil fields.
Iran has had a deep suspicion of Britain since the 19th century, when Britain and Russia jostled for diplomatic and military influence in Persia during the so-called Great Game.