Iranian officials and state media are reporting that two security guards have been killed in a suicide attack outside police headquarters in the southeastern port city of Chabahar.
Rahmdel Bameri, Chabahar's acting governor, was among the Iranian officials who said two victims were killed by the December 6 car-bomb attack.
Earlier reports said at least three people had been killed and more than two dozen injured by the explosion.
Bameri also suggested that more than one assailant was involved in the attack.
"The terrorists exploded a car carrying explosives at the gate of the [police] headquarters," Bameri was quoted as saying by the official government news agency IRNA.
Mohammad Hadi Marashi, the deputy governor in charge of security, said the assailants tried to enter the city's police headquarters but "they were prevented by the guards and they detonated the car bomb."
State television reported shooting in the area shortly after the explosion.
In an online communique, the Sunni jihadist group Ansar al-Furqan claimed responsibility for the attack, according to the Washington-based SITE Intelligence Group, which monitors online extremist activity.
Al-Furqan in 2017 claimed responsibility for bombing an oil pipeline in the southwestern province of Khuzestan.
Meanwhile, Iranian Foreign Minister Mohammad Javad Zarif claimed that those behind the attack were backed by foreign countries and would be brought to justice.
"Foreign-backed terrorists kill & wound innocents in Chabahar," Zarif said on Twitter on December 6.
"As we've made clear in the past, such crimes won’t go unpunished: In 2010, our security services intercepted & captured extremists en route from UAE," Zarif said in what appeared to be a reference to the 2010 capture of Sunni insurgent leader Abdolmalek Rigi.
Iranian authorities said Rigi who headed the militant group Jundollah was captured on a flight from Dubai to Kyrgyzstan. He was later hanged after a revolutionary court convicted him of dozens of charges, including involvement in the killings of dozens of Iranian security officers.
"Mark my words: Iran WILL bring terrorists & their masters to justice," Zarif said on Twitter.
Videos posted online by Iranian news agencies, purportedly from Chabahar, showed thick smoke rising in the area after the blast.
Chabahar is a key port city on the Gulf of Oman about 100 kilometers west of Iran's border with Pakistan.
It is located in Iran's southeastern region of Sistan-Baluchistan, home to a Sunni Muslim minority in largely Shi'ite Iran.
The region has long been plagued by violence blamed on drug smugglers and militant separatists.
Suicide attacks are rare in Iran.
Mohammad Pakpur, the commander of the ground forces of Iran's Islamic Revolutionary Guards Corps (IRGC) said the attack had failed.
"This was a blind terrorist attack," Pakpur told the semiofficial Tasnim news agency. "It had no results for the terrorists.”
Pakpur also said several hours after the explosion that calm and security had returned to the city of Chabahar.
There was no immediate claim of responsibility for the attack.