"Good clues have been obtained and hopefully with the public's cooperation ... we will get to the main leads," Ashtari told the state news agency IRNA. He added that more suspects have been identified and are being sought.
At least 48 people were injured in Thursday's suicide car bomb attack which targeted a police headquarters in the port city of Chabahar in southeast Iran. According to state media, the people behind the attack are from a Sunni extremist group.
Suicide bombings are rare in Iran, which is a Shia majority country. However, in recent years, extremist Sunni groups have carried out several attacks on security forces in the Sistan-Baluchestan province where Chabahar is located.
The U.S.-based SITE Intelligence Group and Iranian state media reported that Sunni Baluch militant group Ansar al-Furqan had claimed responsibility for the attack.
Tehran accuses its Sunni-led regional rival Saudi Arabia and the United States of funding Sunni militants, a charge Riyadh and Washington deny.
Iran has threatened to hit militant bases in neighboring Pakistan unless Islamabad takes action to secure its border area, which Tehran says has become a safe haven for anti-Iran groups to operate.
The majority of Sunnis in the country live Baluchistan, which is considered the most desolate, underdeveloped, and poorest region of Iran.