Iran has accused the UK of co-operating with bombers who killed eight people in attacks in the restive south-western city of Ahwaz on Tuesday.
"Britain must respond to the doubts of Iranians concerning the events," said Foreign Minister Manouchehr Mottaki.
Mr Mottaki said the masterminds of the bombing "or people of their mind" had been photographed with UK officials.
A UK Foreign Office spokesman in London has denied the accusation, saying Britain condemned terrorism.
"Any linkage between HMG (Her Majesty's Government) and these terrorist attacks is completely without foundation," said the official.
A little-known ethnic Arab separatist group has said it was behind the blasts inside a private bank and state environmental agency on Tuesday.
"Our heroes... in the military wing of The Arab Struggle Movement for the Liberation of Ahwaz attacked and destroyed the dens of the occupying enemy," a statement posted on a website said.
British 'co-operation'
Speaking at a press conference in Tehran, Mr Mottaki claimed Britain supported such groups.
"It is clear for our officials and intelligence centres that the United Kingdom co-operated and had a hand in these bombings either in London or Basra," Mr Mottaki told a news conference in Tehran.
"We hope that British officials would have a clear response in that regard."
Mr Mottaki said the attackers had been helped by British army commanders in southern Iraq.
"We hope British officials take this seriously, put it on their agenda and act accountably," he added.
The oil-rich province of Khuzestan, which borders Iraq and is home to about two million ethnic Arabs, was rocked by a wave of unrest last year, including bomb blasts in June and October.
The government blamed the attacks on the UK, whose forces are just across the border, but British officials again denied involvement.
In November, protests erupted in Ahwaz after ethnic Arabs accused authorities of discrimination.
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