The incident happened in the town of Saravan on Saturday night after the Iranian forces tried to prevent the terrorists from entering the country.
The terrorists then fled to the other side of the border after the confrontation.
Earlier reports had put the death toll at six, but police announced on Sunday morning that one border guard, Reza Borji, was resuscitated in the hospital.
Iran’s police said in a statement that such attacks will not go unanswered.
No group has so far claimed responsibility for the attack.
Iran’s Foreign Ministry spokesman Nasser Kanaani strongly condemned the terrorist attack, and urged Pakistani authorities to do more to ensure security along the border.
Spokesperson of Pakistan’s Ministry of Foreign Affairs, Mumtaz Zahra Baloch, in a statement condemned the attack, saying that Islamabad is committed to cooperation with Tehran against terrorism, IRNA reported.
Saravan is only 40 kilometers away from the common border with Pakistan. The border region has over the past years been the scene of clashes between Iranian security forces and terrorist groups and drug traffickers.
Last month, a senior Iranian police officer was killed in a terrorist attack in the province after unidentified assailants launched an attack on him.
Colonel Alireza Shahraki, chief of the Iranian Police Criminal Investigation (CID) Department in Saravan, was fatally shot on April 30 after unknown gunmen sprayed bullets on his car in an early morning ambush at a crossroad.
Back in 2018, 12 Iranian border guards were kidnapped by members of the Jaish ul-Adl terrorist group, which were based on Pakistani soil.
In April 2017, 11 of the border guards were killed in an ambush claimed by the terrorist group near the town of Mirjaveh in Sistan and Baluchestan, which borders both Afghanistan and Pakistan.