BEIRUT (AP) — Syrian opposition activists and an independent monitor say government forces battling insurgents in southern Syria have carried out a series of airstrikes on a city that has been declared a safe zone under a recent Russia-sponsored deal.

The Britain-based Syrian Observatory for Human Rights says 12 airstrikes and at least nine barrel bombs hit rebel-held parts of the city of Daraa amid intense clashes with insurgents.

The activist-run Step News Agency and Qasioun News Agency also reported Wednesday's clashes and shelling in the city.

Russia, Iran and Turkey agreed to establish the zones in Syria, signing on to a Russian plan under which the Syrian air force would halt flights over designated areas across the country.

This week's clashes are among the worst violations of the "de-escalation" agreement.