Scores of people have been killed and many more injured in army and rebel attacks in different locations in Syria, activists said, hours before a visit to the Syrian capital by Iran's foreign minister.

Army artillery shelling and air strikes on Wednesday targeting Douma, 10km from central Damascus, killed at least 37 people, including women and children, and injured more than 120, the UK-based Syrian Observatory for Human Rights reported.

Activists also reported that 13 people were killed in air strikes in neighbouring Saqba.

The Syrian Observatory said at least 12 people were killed in rocket attacks by rebels targeting several neighbourhoods in Damascus, including Abu Romaneh and Bab Touma in the centre.

Syrian state TV reported that five civilians were killed and 55 others injured in rebel attacks, saying, "Terrorists launched mortar attacks targeting a number of residential districts in Damascus."

The deaths came as Syria's warring parties declared a 48-hour ceasefire in a front line area after a month of unprecedented mediation from Turkey and Iran, backers of rival sides in Syria.

The ceasefire halted fighting between rebels on the one hand, and the army and its Lebanese Hezbollah allies on the other, in the rebel-held town of Zabadani and in a pair of Shia Muslim villages in Idlib province.

Iranian visit

Foreign Minister Mohammad Javad Zarif arrived in Damascus from Beirut on Wednesday and met Syria's President Bashar al-Assad.

Zarif called on regional countries to "fight terrorism and extremism".

"I say to the other [regional] players and to our neighbours that now is the time to care about the truth, answer the aspirations of the Syrian people and work to fight terrorism, extremism, and sectarianism," he said.

He did not give details on his discussions with Assad on finding a solution to Syria's four-year war, only describing the exchange of views as "good".

An Iranian foreign ministry spokesman had said a new Iranian peace plan was based on "respect for the Syrian people's legitimate right to reforms and to decide their own future".

An Iranian foreign ministry spokeswoman said he would be discussing a new plan to resolve the war.

In another development, at least 39 Syrian forces were killed when ISIL attacked the army's Kweires airport and the air force academy in the suburbs of Aleppo, the Syrian Observatory reported. At least 33 ISIL fighters were also reportedly killed during clashes.

The airport, located in the east of Aleppo city near the ISIL-controlled al-Bab town, has been besieged since 2013. It is estimated that there are between 300 to 500 troops inside the airport.

The Syrian Observatory also reported that at least 20 people were killed by government loyalists as they attempted to flee Idlib city to its suburbs.