Iranian police have defused a large bomb under a bridge in the tense southwestern city of Ahvaz, just days after a double bombing there killed six people and wounded more than 100.
The latest incident on Tuesday brought renewed insinuations from Iranian President Mahmud Ahmadinejad that Britain might be fanning tensions in the area, which was the scene of riots by Arab residents earlier this year.
Iran's judiciary maintained that "foreign states" were involved in ongoing unrest in the oil-rich province, and a senior deputy alleged explosives and weapons seized in the area had come from British troops based just across the border in Iraq.
Police told state television they acted on a tip-off from local residents who spotted a suspect package under a busy bridge in Ahvaz, the capital of Khuzestan province dominated by minority Arabs.
The report said the package - wired up and containing eight anti-personnel mines, around one kilogramme of TNT, one stun grenade and a large number of fuses - was successfully defused late on Monday.
Two bombs exploded outside a crowded market in Ahvaz late Saturday. Funerals of the six victims were held on Monday, but the death toll could still rise given that several of those injured remain in critical condition.
Ahmadinejad suggested the UK
is stirring tensions
"More than 20 people have been arrested in connection with these incidents in Ahvaz," Intelligence Minister Gholam Hossein Mohseni Ejeie told the student news agency ISNA, but gave no further details.
However, the Kayhan daily quoted Ahvaz Governor Nasser Sudani as saying Iranian intelligence had arrested a man linked to Saturday's bombings who "admitted to being trained by British forces in Iraq".
Ahvaz has been hit by a wave of unrest this year, including ethnic riots in April over reported plans to change the ethnic make-up of the area and a series of car bombings prior to Iran's presidential elections in June.
Iranian officials have in the past blamed Arab separatist groups or Iranian opposition militants they say enjoy backing across the border in Iraq.
Iranians of Arab descent make up about 3% of the population of the Islamic republic.
Hardline President Ahmadinejad was quoted as saying "we have not found any proof that Great Britain is not involved in the events in Ahvaz and we have not seen anything that would dissipate our doubts about that country.
"There are signs concerning (British) involvement in these incidents and our doubts and the signs are serious. Our security officials are examining the incidents and I hope they will soon give their results," he told the Mehr news agency.
"Iran's security and intelligence officials have come across British footprints"
Ahmadinejad had already said he suspected British involvement in Saturday's bombing, an allegation that came hot on the heels of British complaints of Iranian meddling in Iraq.
"Iran's security and intelligence officials have come across British footprints" in past attacks in the area, he said, adding that "we are strongly suspicious of British forces committing
Britain has roundly denied the allegations and condemned the
It says it has also told Tehran "the British government and British forces in Iraq stand ready to help in any way they can to prevent attacks of this kind or identify those responsible and bring them to justice".
Britain's charge d'affaires in Tehran was summoned to the foreign ministry on Monday to hear a complaint over British allegations that Iran is meddling in Iraq.
British Prime Minister Tony Blair and other senior officials said last week there was evidence that a series of deadly attacks on British troops in southern Iraq lead back to Iran and the Lebanese Shia resistance group Hizb Allah.
Iran has dismissed those allegations as "absurd and baseless".