BEIRUT — Syria said Monday it is prepared to hold talks with the armed rebels bent on overthrowing President Bashar Assad, the clearest signal yet that the regime is growing increasingly nervous about its long-term prospects to hold on to power as opposition fighters make slow but persistent headway in the civil war.

The offer, by Foreign Minister Walid al-Moallem during a visit to Moscow, came hours before residents of Damascus and state-run TV reported a huge explosion and a series of smaller blasts in the capital, followed by heavy gunfire.