Six dead in clashes at Iran-Pakistan border
Iran's Revolutionary Guards described the incident as a terrorist attack, and said three people were killed by Iranian security forces in a "firm and timely response".
The cross-border attack comes a day after Iran's security forces seized a large amount of weapons stock and ammunition from militants in the province. Sistan-Baluchestan is majority Sunni and home to the Baluchi speaking ethnic minority.
From 2005 to 2010, the militant Jundallah group - made up of Baluchi-speakers who are found on both sides of the Iran-Pakistan border - waged an insurgency in Sistan-Baluchestan.
Violence in the area was largely curbed after its leader Abdulmalik Rigi was killed in 2010.
The province also lies on a major smuggling route for Afghan opium and heroin.
Violence has sporadically cropped up since 2010 in Sistan-Baluchestan. In April 2017, ten Iranians were killed by militants in Mirjaveh.
Iran has criticised Pakistan for supporting the Jaysh al-Adl - formed in 2012 by prior Jundallah members - which it says is tied to al-Qaeda and is responsible for numerous attacks in the province.
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