A car loaded with explosives blew up near a bus carrying members of Iran's elite Revolutionary Guards in southeastern Iran, killing 18 of the Guards, the state-run news agency reported Wednesday.
The car stopped in front of a Guards' bus near Zahedan, the capital of Sistan-Baluchestan Province, the official Islamic Republic News Agency reported. It called the apparent attack a terrorist operation and said the car's occupants fled on motorbikes seconds before the car exploded.
"This blind terrorist operation led to the martyrdom of 18 citizens of Zahedan," IRNA quoted a Guards commander, Qasem Rezaei, as saying.
State-run television said the bus had been taking the Guards personnel to work when the attack occurred.
There was no immediate claim of responsibility but Rezaei blamed "insurgents and elements of insecurity" for the attack.
Hossein Ali Shahriyari, a lawmaker representing Zahedan, told an open session of the parliament Wednesday that "insurgents and drug traffickers" were behind the attack.
Shahriyari called lawless regions in southwestern Pakistan a safe haven for Iranian insurgents and drug traffickers, and called on the government to take up the issue with Islamabad.
"Why doesn't our foreign diplomatic apparatus deal with Pakistan, whose soil has turned into a safe heaven for insurgents?," he asked. His speech was broadcast live on state-run radio.
Majid Razavi, an Interior Ministry official, said one of those behind the explosion was arrested less than one hour after the attack.
"One of the perpetrators of this morning's explosion was arrested," IRNA quoted Razavi as saying, but it did not elaborate.
The explosion occurred around 6:30 a.m. in Ahmadabad district on the outskirts of Zahedan, IRNA said.
The passenger car stopped in the middle of the road, forcing the bus loaded with Guards to stop, the news agency said. The occupants then fled as the car exploded, reports AP.
Zahedan and its surroundings, which lie near Iran's borders with Pakistan and Afghanistan, have been the scene of clashes between police and drug smugglers in the past.
Three small explosions injured two people in Zahedan last June, but Wednesday's explosion was the deadliest in years.
The explosion comes at a time of high tension between Iran and the United States over insurgents in Iraq and Iran's controversial nuclear program.
Unofficial reports have emerged in recent weeks accusing the U.S. of meddling at Iran's borders and provoking ethnic and religious violence to undermine the Iranian government. However, there have been no official Iranian statements nor any evidence to back up the reports.