ISIS said it was behind a bombing south of the Syrian capital Damascus the day before that killed at least six people and wounded 20.

Thursday’s explosion was near the Sayeda Zeinab mausoleum in Damascus, Syria’s most visited Shia pilgrimage site, and came on the eve of the annual Shia Ashura commemoration.

In a statement on the Telegram messaging app, the extremist group said some of its fighters breached tight security imposed by the Syrian regime and militias guarding the mausoleum area.

It said “they were able to park and detonate a motorcycle bomb ... during a gathering of Shia pilgrims.”

The authorities had tightened security measures around the mausoleum for the 10-day Ashura commemoration, among the most important in Shia Islam.

In the same message on Friday, ISIS claimed “another bomb attack” it said had targeted “a bus transporting Shia pilgrims in the same area, wounding at least two and destroying the vehicle.”

On Tuesday, an explosion in a car in the same area of the Syrian capital had wounded two civilians, official media cited a security official as saying.

Shia shrines are a frequent target of attacks by Sunni Muslim extremists of the ISIS group, not only in Syria but also in neighboring Iraq.