At least three people, including a child, have been injured in an attack by armed men at an election campaign office run in support of Mahmoud Ahmadinejad, Iran's president.

The shooting took place in the southeastern city of Zahedan on Friday, a day after a bomb attack at a mosque in the city killed at least 20 people and injured dozens more.

Mohammad Reza Zahed Sheikhi, who runs the election office, said: "Three knife-wielding people on motorbikes stopped outside the centre on Saadi Street, cursed, made threats and tore up billboards."

He said that as the campaign workers went towards them to protest "the attackers pulled out guns and shot at them".

Child wounded

IRNA, Iran's state news agency, said the attack took place at around 1900 local time (1430 GMT).

Sheikhi said a child was also shot in the stomach and was undergoing surgery.

Two campaign workers sustained arm, stomach and shoulder wounds and were taken to hospital, he said.

"The men ran away, but the police chased and arrested them," Sheikhi said.

Zahedan is the regional capital of the Sistan-Baluchestan province which borders Pakistan and Afghanistan.

Iran goes to the polls in presidential elections on June 12.