Update: The death toll of a suicide attack in the southeast of the country rose to 41, according to Iran news agency Fars on Wednesday.
Earlier, reports said that 27 members of Iran's military were killed in a suicide attack the southeast of the country.
The attack happened on the road between the cities of Zahedan and Khash, a volatile area near the Pakistan border where militant groups and drug smugglers frequently operate.
Another ten members of the guards were also wounded in the attack, which targeted a bus transporting the security force, Fars reported.
Jaish Al Adl (army of justice) has "issued a statement officially taking responsibility for the terrorist attack" in southeastern Iran, Fars said.
The group is blacklisted as a terrorist group by Iran, which was formed in 2012 as a successor to the group Jundallah that waged a deadly insurgency over the previous decade.
Iran will take revenge for a suicide attack against the Revolutionary Guards, foreign ministry spokesman Bahram Qassemi said on Wednesday, according to the Fars news agency.
"The self-sacrificing military and intelligence children of the people of Iran will take revenge for the blood of the martyrs of this incident," Qassemi said, according to Fars.