* At least 28 killed in twin suicide attacks
* Revolutionary Guards among casualties
* Jundollah claims responsibility
* Zahedan MP resigns
(Adds burial ceremony on Saturday, Ban Ki-moon’s statement)
By Parisa Hafezi
TEHRAN, July 16 (Reuters) - Two suicide bombers killed at least 28 people, including elite Revolutionary Guards, at a Shi‘ite Muslim mosque in southeast Iran, an attack Iranian leaders said was backed by the United States.
The Sunni Muslim rebel group Jundollah said it set off the bombs on Thursday, telling Al Arabiya television in an email it had carried them out in retaliation for Iran’s execution in June of the group’s leader, Abdolmalek Rigi.
Jundollah says it fights for the rights of Iran’s Sunni Muslim minority. Iran’s clerical leadership accuses its arch-foe, the United States, of backing Jundollah to create instability in Iran. Washington denies the charge.
The powerful bombs exploded near the Grand Mosque in the city of Zahedan, scattering body parts around the holy site. Jundollah said they were detonated by relatives of Rigi and were aimed at a Revolutionary Guards gathering.
"The group said the suicide attacks were carried out by Abdolbaset Rigi and Mohammad Rigi ... and warned of more operations to come," Dubai-based Al Arabiya said.
Senior lawmaker Alaeddin Boroujerdi said the United States should be held accountable for the "terrorist acts in Zahedan" because of its support for Jundollah, the IRNA news agency said.
"Once more the wicked hand of America appeared out of the sleeves of ignorant and mercenary people," cleric Kazem Sediqi said in a Friday sermon broadcast live on state radio.
Iran is locked in a dispute with the United States and its allies over Tehran’s nuclear programme, which the West says is designed to produce nuclear weapons and Iranian officials say is for purely civilian purposes.
THREE DAYS’ MOURNING
The head of the medical school at Sistan-Baluchestan province, Mansour Shakiba, said the attacks had killed at least 28 people and injured more than 169, the semi-official Mehr news agency reported.
Iran’s deputy interior minister in charge of security, Ali Abdollahi, said a number of Revolutionary Guards had been killed and injured, the semi-official Fars news agency reported.
Iran announced three days of public mourning in the province and said the bodies of those killed would be buried on Saturday, news agencies reported.
Predominantly Shi‘ite Muslim Iran arrested Rigi in February, four months after Jundollah claimed responsibility for a bombing which killed dozens of people, including 15 members of the Guards.
Zahedan is the capital of Sistan-Baluchestan province, which shares a border with Pakistan. The province faces serious security problems and there are frequent clashes between police and drug dealers and bandits.
Zahedan’s representative to parliament Hosseinali Shahriari resigned over the attacks "because of the inability of authorities to maintain security in his constituency", the website of Iran’s English-language Press TV reported on Friday.
In Washington, U.S. Secretary of State Hillary Clinton condemned the attacks "in the strongest possible terms".
"This attack, along with the recent attacks in Uganda, Pakistan, Afghanistan, Iraq and Algeria, underscores the global community’s need to work together to combat terrorist organisations that threaten the lives of innocent civilians all around the world," Clinton said in a statement.
U.N. Secretary-General Ban Ki-moon also condemned the attacks.
"This senseless act of terrorism at a place of worship makes it all the more reprehensible," he said in a statement.
Iran says Jundollah has links to Sunni Islamist al Qaeda and in the past has accused Pakistan, Britain and the United States of backing Jundollah to create instability in southeast Iran.
All three countries have denied this, and Jundollah denies having any links with al Qaeda.
In May 2009, a suicide bomber killed 30 people and wounded more than 120 in an attack on a mosque in Zahedan.
Iran is grappling with ethnic and religious tensions in the southeastern province, where authorities have responded to attacks by Sunni rebels with a spate of hangings. Rights groups and the West have condemned the executions.
Iran rejects allegations by rights groups that it discriminates against ethnic and religious minorities. (Writing by Parisa Hafezi; editing by Andrew Roche)