The Revolutionary Guards said in a statement that a vehicle loaded with explosives had targeted a bus carrying affiliated border guards.
Known for being volatile, militant groups and drug smugglers frequently operate in the area.
No group immediately claimed responsibility for the attack.
Twelve members of the Guards were among 25 people killed last autumn by gunmen on a military parade in the city of Ahvaz in the southwest.
"This terrorist act happened a short time ago and according to reports at least 20 have been martyred and 20 have been wounded", an informed source told IRNA.More news: Former US Air Force officer Monica Witt charged with spying for Iran
The statement did not identify the "hegemonic powers", but Iran's foreign minister linked the bombing to a US-led conference on the Middle East taking place in Warsaw, Poland, that will include discussions about Iran's activities in the region.
Jaish al-Adl, formed in 2012, is a successor to the extremist group Jundallah (Soldiers of God), which has carried out a spate of attacks on Iranian security forces in recent years in the southeastern province of Sistan-Baluchistan.
Jaish al-Adl emerged as the main armed opposition movement in the southeast after members of another Sunni group, Jundullah, joined it after their leader was captured on a plane in 2010. Saudi Crown Prince Mohammed bin Salman for instance in a 2017 interview suggested the kingdom knew it was a "main target of Iran". Prince Mohammed is due in Pakistan, a major recepient of the kingdom's largess, in the coming days.
It came on the same day that a conference convened by the U.S. in Warsaw was to include discussions on what Washington describes as Iran's malign influence across the wider Middle East. President Donald Trump, who campaigned on a promise of tearing up Tehran's nuclear deal with world powers, withdrew the US from the accord last May.
Amid the new tensions, Iran's already-weakened economy has been further challenged.More news: Texas couple jailed after children found neglected
Iran's foreign minister, Mohammad Javad Zarif, described the conference convened by the United States as the Warsaw Circus, and said it was "no coincidence that Iran is hit by terror on the very day" that the talks began.
Foreign Ministry Spokesman Bahram Qassemi condemned the attack and said the victims will soon be avenged.
"Especially when cohorts of same terrorists cheer it from Warsaw streets & support it with twitter bots?"
Ten members of the Guards were also wounded in the attack, which targeted a bus transporting the security force, according to Fars News Agency.
"I believe it's dead on arrival or dead before arrival", he said at a news conference before the bombing.More news: Morgan Stanley to buy Calgary-based Solium Capital for $1.1 billion
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