On Thursday, Islamabad designated the Zainebiyoun Brigade, an Iran-backed Shiite militant group, as a terrorist organization.

Formed by the IRGC after the Syrian civil war began, the Zainebiyoun Brigade, also known as Liwa Zainebiyoun, mobilized Pakistani Shiite militants who were then sent to fight forces opposed to Syrian ruler Bashar al-Assad, a close ally of Iran and Russia.

The Iranian regime has been an active actor in the Syrian conflict which started in 2013 and has so far claimed the lives of around 500,000 people, at least 60 percent of whom were civilians.

To help maintain Assad’s rule, Iran dispatched its other proxies to Syria as well, including Hezbollah, Iraq’s Nujaba Movement, and also the Fatemiyoun Division, which was composed of Afghan Shiite fighters.

Iranian officials and state media frequently credit former IRGC commander Qassem Soleimani as the man behind launching, training and funding all these militant groups. Soleimani, who served as the Iranian regime’s top military and intelligence operator in the Middle East, was killed in a US drone strike in January 2020 in Iraq’s capital, Baghdad.

Observers contend that Tehran’s attempts to mobilize Shiite militant groups, such as Zainebiyoun, and their active participation in the Syrian war fanned the flames of sectarian violence in the Middle East, provoking Sunni communities to employ a similar strategy in the region.

Pakistan’s decision to designate the Zainebiyoun Brigade threatens to further strain ties between Tehran and Islamabad. The two countries witnessed unprecedented tensions in January when the IRGC attacked positions in Pakistan in what it called an attempt to target terrorists. Pakistan retaliated by attacking locations in southeastern Iran.

Days after the mutual attacks, Pakistan's Counter-Terrorism Department (CTD) announced it arrested a suspect in the 2019 assassination attempt on a top Pakistani cleric, saying the suspect was a "trained terrorist" who belonged to the Zainebiyoun Brigade.

Pakistan’s CTD added that Syed Mohammad Mehdi was arrested in an operation at a bazaar in Karachi, accusing him of targeting clerics in the provincial capital and of working for Iranian intelligence.

The insurgent Sunni Baluch group known as Jaish al-Adl (Army of Justice) has been a source of tension between Iran and its nuclear neighbor, Pakistan, for years, labeled as a terrorist organization by Iran, Pakistan, and the United States.

Iranian officials have on several occasions in the past decade, including in 2019, complained that Islamabad has taken no action against the members of Jaish al-Adl finding refuge in its territory despite Iran's provision of relevant information, including locations of the militants’ hideouts.

A militant group advocating for enhanced rights and improved living conditions for the Baluch ethnic minority, Jaish al-Adl has recently intensified its operations against Iranian security forces in Sistan and Baluchistan, an economically challenged province in southeastern Iran adjacent to Afghanistan and Pakistan and home to a substantial Sunni community.

On Tuesday, six law enforcement officers were killed by Jaish al-Adl militants during an ambush on police vehicles along the Sib and Suran county route. The group also launched simultaneous attacks against military posts in Chabahar and Rask last week, killing 16 police forces.