The suicide attack, which targeted a bus carrying Islamic Revolutionary Guards Corps personnel, claimed the lives of 27 people and injured dozens of others in southeastern Iran on February 13.
Iran also accuses regional rival Saudi Arabia of promoting violence among members of Iran's Sunni Muslim minority.
Brigadier General Mohammad Pakpour, the commander of the IRGC's ground forces, made the statement in a ceremony commemorating the martyrs of the attack which hit a bus carrying Iranian border guards in Zahedan-Khash road last Wednesday.
But on Sunday it said the attack was carried out from neighboring Pakistan.
Three elements of the terrorist team were from the Sistan and Balouchestan region, the commander said, adding that two of them have been arrested and the other, who is at large, will soon be detained.
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Previously, IRGC chief Mohammad Ali Jafari blamed Pakistan for its alleged backing of jihadists who wage terror in his country, calling on Islamabad to tighten its policy towards the al-Qaeda-linked Sunni Jaish ul-Adl terrorist group, which claimed responsibility for the bombing.
On Wednesday night when a number of IRGC forces were traveling between the cities of Zahedan and Khash, in Sistan and Balouchestan, their bus was hit by the suicide vehicle bomb attack.
But security forces had been "fully prepared" on that day, he said.
Both Iran and India condemned Pakistan over the act and sought steps on its behalf against terrorists.