Four Pakistanis were killed and two were injured late on Tuesday night, when Iranian forces opened fire in the restive southwestern province of Balochistan in Pakistan, Reuters reported.

The shooting took place near the Pakistan-Iran border, in Washuk District, confirmed Umar Jamali, additional deputy commissioner.

Naeem Umrani, deputy commissioner Washuk, said an investigation is being initiated to determine the reason for the shooting.

Former Iranian President Ebrahim Raisi visited Pakistan in April on a three-day official visit as the two Muslim neighbours seek to mend ties after unprecedented tit-for-tat military strikes this year. Raisi's visit was seen as a key step towards normalising ties with Islamabad.

Iran and Pakistan have had a history of rocky relations, but missile strikes in January were the most serious incidents in years, with Pakistan recalling its ambassador to Tehran and not allowing his counterpart to return to Islamabad, as well as cancelling all high-level diplomatic and trade engagements.

Swift efforts to lower the temperature subsequently led to assurances that they respected each other's sovereignty and territorial integrity, as well as vows to expand security cooperation and requests for envoys to return to their posts.

Islamabad said it hit bases of the separatist Baloch Liberation Front and Baloch Liberation Army, while Tehran said it struck militants from the Jaish al-Adl (JAA) group.

The militant groups operate in an area that includes Pakistan's southwestern province of Balochistan and Iran's southeastern Sistan-Baluchestan province. Both regions are restive, mineral-rich and largely underdeveloped.

(Report by Reuters)