Syrian government warplanes carried out several air strikes in the Eastern Ghouta area east of Damascus on Sunday, a day after the Syrian military declared a cessation of hostilities in the area, the Syrian Observatory for Human Rights said.

The British-based monitoring group said Saturday had been relatively calm after the ceasefire took effect with isolated incidents of shellfire.

On Sunday, six air strikes hit the towns of Douma and Ain Terma in opposition-held Eastern Ghouta, it reported.

The Assad regime announced Saturday ceasefire in the East Ghouta region of the capital Damascus, according to the regime's Defense Ministry.

The ministry said in a statement that the regime stopped its "military operations" in some areas of the East Ghouta region adding: "Any violation [of the ceasefire] will be responded to accordingly."

Syria has been locked in a vicious civil war since early 2011 when Bashar Assad's regime cracked down on pro-democracy protests, which erupted as part of the Arab Spring uprisings.

Since then, more than 400,000 people have been killed and more than 11 million have been displaced, 6.3 million internally and 5.1 million externally, across the war-battered country, according to the U.N.