TEHRAN, Feb. 14 (Xinhua) -- Five people were arrested on suspicion of involving in a car bomb attack in Iran's southeastern city of Zahedan on Wednesday morning which killed at least 11, the official IRNA news agency reported.

    "Five people suspected of involvement in the huge blast had been arrested," said Soltan-Ali Mir, director-general for political affairs in office of Sistan-Baluchestan province's governor.

    Soltan-Ali Mir was quoted as saying that "two of the five suspects were arrested with the help of pedestrians who tipped the police."

    Several hand-grenades and a video camera were seized from the two armed men and the three other suspects were arrested hours ago, he added.

    An explosive-laden car exploded as a bus, belonging to ground forces of Iran's Revolutionary Guards (IRGC), passed by, killing at least 11 people, IRNA said, adding that it was not clear if those killed were members of the IRGC guards.

    The explosion occurred around 6:30 a.m. (0300 GMT) in Ahmadabad district on the outskirts of Zahedan, capital city of Sistan-Baluchestan province.

    Earlier, some reports said that 18 people were killed in the blast and some said eight. Due to disordered statistics, the exact casualty number was still uncertain yet.

    The state-run television reported that the bus was carrying the guards personnel when the attack occurred. Footage showed that the bus had been blown down into a contorted frame of wreckage.

    According to a witness, the explosive-laden car parked on the side of a road. Armed men in two motorcycles opened fire at the moving IRGC bus as it approached the car and they set off the bomb.

    There was no immediate claim of responsibility for the attack but Hossein Ali Shahriyari, a lawmaker representing Zahedan, accused "insurgents and drug traffickers" of being behind the attack, blaming the security forces and policy for not carrying out their responsibilities.

    Sistan-Baluchestan province borders both Afghanistan and Pakistan. Iranian security forces usually clash with local armed groups involved in drug smuggling.

    Sistan-Baluchestan and its close province of Kerman have been hit by a string of attacks and kidnappings in the past years, which the Iranian authorities blamed on a Sunni group called Jundallah.

    Earlier this year, four members of Iranian security forces were killed in Zahedan when armed men opened fire at their vehicle.