DAMASCUS -- A big blast was heard near the high-end Four Seasons Hotel in the heart of the Syrian capital Damascus on Sunday afternoon, witnesses said.

No details from official media have been disclosed yet, but the Lebanese NBN TV said the blast was caused by an explosive device planted at Beirut Street of Damascus near the hotel.

The TV said two people were injured.

The blast occurred while the Syrian opposition is currently holding a conference for "rescuing Syria."

It also comes as part of the ongoing violence that has engulfed most of the Syrian areas after 19 months of crisis.