Two explosions rattled the Malek Ashtar base of Iran’s Revolutionary Guard’s paramilitary force Basij militia in southeast of the capital Tehran late Friday.

Videos shared on social media showed fire and smoke billowing from the base.

Iranian official media and websites affiliated with the Revolutionary Guard have remained silent on the incident.

Since May, there have been several attacks and mysterious incidents against Revolutionary Guard (IRGC) officers. One key commander was assassinated in Tehran on May 22 in broad daylight, while another was said to have fallen from the roof of his house and died a few days later. Iran has blamed Israel, in what has damaged the reputation of Iran’s intelligence and security organizations.

In a statement, the exiled Iranian opposition group Mujahedin-e Khalq Organization (MEK) claimed the attack was carried out by “revolutionary cells”, a term it often uses to characterize anti-regime acts and protests in Iran. The group which used large-scale violence in the 1980s and 1990s in its fight against the Islamic Republic, later distanced itself from armed attacks.

In early June, an Iranian hacktivist group reportedly affiliated with the Albania-based MEK, named ‘Uprising till Overthrow’ hacked into and deactivated over 5,000 surveillance cameras and 150 websites and online services of Tehran Municipality.

The MEK was listed by the US from 1997 to 2012 as a ‘foreign terrorist organization,’ but was subsequently removed from the list. The group has cultivated links with many politicians in the US and Europe, paying large sums for attendance or speeches at its rallies.