BEIRUT — The international chemical weapons watchdog said Tuesday that it plans to send a fact-finding mission to Syria to investigate allegations that the government used chlorine gas in attacks against civilians in recent weeks.

The announcement came as mortar fire and a bombing killed more than 50 people in government-controlled parts of Damascus and Homs, underscoring the risk that a prolonged insurgency will continue to bleed areas where rebels are being quashed.

In a statement issued at its headquarters in The Hague, the Organization for the Prevention of Chemical Weapons said inspectors would leave “soon” to verify whether chlorine gas was used in bombs dropped on at least two villages in rebel-held areas of northern Syria.

The Syrian government has agreed to the mission and has promised to provide security in territory under its control, the statement added. But it is not clear how the inspectors will cross dangerous front lines to reach the opposition areas where the attacks occurred.

Although the attacks have not been independently verified, videos posted on YouTube showed scores of civilians gasping for breath in hospitals after reportedly inhaling gases.