DAMASCUS, Syria — Russia and the Arab League proposed Wednesday to broker talks between the Syrian opposition and President Bashar Assad’s regime to try to resolve the country’s civil war, while a government airstrike on a rebellious Damascus suburb killed at least 20 people.

The 23-month-old conflict, which has killed more than 70,000 Syrians and laid waste to the country’s cities, has repeatedly defied international efforts to bring the parties together to end the bloodshed. Wednesday’s offer from Moscow, one of Assad’s closest allies, suggested the regime could be warming to the idea of a settlement as it struggles to hold territory and claw back ground it has lost.