Daesh group said on Friday 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 Shiite pilgrimage site, and came on the eve of the annual Shiite Ashura commemoration.
In a statement on the Telegram messaging app, the jihadist 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 Shiite Islam.
In the same message on Friday, Daesh claimed "another bomb attack" it said had targeted "a bus transporting Shiite pilgrims in the same area, wounding at least two and destroying the vehicle".
Agence France-Presse