"In this suicide attack a auto filled with explosives blew up besides a bus carrying a unit of the Guards' ground forces causing the martyrdom and wounding of a number of the protectors of our Islamic homeland's border", the statement read.
Sistan-Baluchistan is a volatile province near the border with Pakistan, where militant groups and drug smugglers frequently operate.
The Fars news agency said the attack was claimed by Jaish al-Adl, a jihadist group formed in 2012 as a successor to the Sunni extremist group Jundallah, which had waged a deadly insurgency against Iranian targets.
The Guard is a major economic and military power in Iran, answerable only to the country's supreme leader, Ayatollah Ali Khamenei.
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An attack by gunmen on a military parade in the city of Ahvaz last autumn killed at least 25 people, including 12 members of the Guards.
The attack comes as Iranian officials have said they blame Saudi Arabia and the United States for stirring up dissent in the country.
"Foreign-backed terrorists kill & wound innocents in Chabahar".
And in October, Jaish al-Adl kidnapped at least 10 security personnel, including several Revolutionary Guards, at a border post in Mirjaveh.
Iranian Foreign Minister Mohammad Javad Zarif appeared to blame the United States for the attack, citing a US -sponsored conference in Warsaw aimed at rallying support to further isolate Iran. There have been sporadic protests in the country as well, incidents applauded by Trump amid Washington's maximalist approach to Tehran.
On Twitter he asked: "Is it no coincidence that Iran is hit by terror on the very day that #WarsawCircus begins?" "U.S. seems to always make the same wrong choices, but expect different results", Iranian foreign minister Javad Zarif said in reaction to the attack.
"I believe it's dead on arrival or dead before arrival", he said at a news conference before the bombing.