The bomb detonated during evening prayers in the mosque

Three men convicted of bombing an Iranian mosque two days ago have been publicly executed, state media says.

The bombing killed at least 19 people during evening prayers in the south-east city of Zahedan on Thursday.

The three men, who were hanged on Saturday morning near the mosque, were already in custody before the attack.

One Iranian official had earlier accused the US of hiring mercenaries to carry out the bombing - a claim dismissed by Washington.

The men were arrested before Thursday's bombing in connection with other attacks, including a 2007 attack on Iran's Revolutionary Guard in which 11 people died.

Authorities said they were tried and had legal representation.

A spokesman for the Sistan-Baluchestan province's judiciary said the three people "confessed to illegally bringing explosives into Iran and giving them to the main person behind the bombing."

Spokesman Hojatoeslam Ebrahim Hamidi added: "They were convicted of being 'mohareb' (enemies of God) and 'corrupt on the earth' and acting against national security," Irna reported.

Part of a Shia mosque, Amir al-Mohini, was destroyed in Zahedan, a mainly Sunni Muslim city.

A Sunni militant group had claimed responsibility, with Abdel Raouf Rigi, described as a spokesman for the Jundallah group, telling Saudi-owned TV channel Al-Arabiya that a suicide bomber had targeted a secret meeting of Iran's elite Revolutionary Guards inside the mosque.

When an Iranian official accused the US of being behind the bombing, a US state department spokesman denied any involvement.

The bombing, described by the Iranian media as a suicide attack, came at a time of heightened tension ahead of upcoming presidential elections .

A day after the bombing, the President Mahmoud Ahmadinejad's Zahedan campaign office was attacked by gunmen.

The government has warned that foreign powers are trying to sabotage the process, the BBC's Jon Leyne in Tehran says.

With President Ahmadinejad facing an increasingly tough battle for re-election, any growing sense of crisis will certainly not do any harm to this fiercely nationalist and populist leader, our correspondent says.