The assault came as the troops were returning from a border patrol mission, the Guards said in a statement.
"In this terrorist attack 27 of Islam's brave warriors were killed and 13 were wounded," the statement read, accusing "world domination and Zionist intelligence agencies" of supporting the attackers.
Earlier the official IRNA news agency said, "The suicide attack on an Islamic Revolutionary Guards Corps personnel bus happened on the Khash-Zahedan road."
A picture released by the semi-official Fars news agency showed a hulk of twisted metal lying by the side of a road, unrecognisable as a bus.
The attack happened when "a car filled with explosives blew up besides a bus", the Guards said.
"Mercenaries of intelligence agencies of world arrogance and domination," carried out the attack to counteract "the victory of the 40th anniversary of the Islamic revolution", they added.
His arrival triggered the start of the Islamic Revolution and led to the creation of the Islamic Republic.
The SITE Intelligence Group reported that the attack was claimed by Jaish al-Adl, a jihadist group formed in 2012 as a successor to the Sunni extremist group Jundallah (Soldiers of God), which waged a deadly insurgency against Iranian targets over the past decade.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)