Damascus (AFP) - After a long period of relative calm, Syria's capital is coming under daily mortar and rocket fire from rebels seeking to make the regime ease its attacks on areas they hold near Damascus.

"It is in response to regime air raids on rebel districts around Damascus," said Rami Abdel Rahman, director of the Syrian Observatory for Human Rights.

Rebel bombardments of the city "have caused a total of 21 deaths in recent days", he said.

Launched from Eastern Ghouta, a woody region east of Damascus where rebels have held off regime efforts to dislodge them, the mortar fire targets several districts, including upmarket Malki where the presidential place is located.

"After a long period of calm, mortar fire began on the Saturday after (the Moslem holiday of) Eid," on August 2, said Abu Hisham, owner of a women's clothes shop in Al-Salhiyeh shopping district in the heart of the city.

"Yesterday and the day before (Tuesday and Wednesday) the noises were new and terrifying. We heard the whistling of the mortar then the explosion."

- Presidential palace -

Rebel chief Abdel Rahman al-Shami said the mortar rounds are in answer to "an escalation of bombardments" by President Bashar al-Assad's forces against opposition strongholds.

"The rebels are trying to aim at military targets in Damascus," said the Jaysh al-Islam leader, speaking to AFP from Douma, a town northeast of the capital held by the rebels and regularly raided by regime warplanes.

Assad's forces have also stepped up bombardments of Kafar, east of Damascus, as well as Mleiha and Douma, he said.

Last Sunday, regime warplanes raided Eastern Ghouta, Kafar Batna and Douma, killing at least 64 people at a market, including 11 children, according to the Britain-based Observatory.

Jaish al-Islam (Army of Islam) and another rebel group, Ajnad al-Sham (Soldiers of Damascus) have been firing 107 mm and 120 mm mortars into Damascus, Shami said.

He said Ajnad al-Sham fighters had been targeting the presidential palace in Malki and military positions.

Story continues

"This will carry on as long as bombardments continue" against rebel areas, Shami said.

A leader of Ajnad al-Sham said on Facebook that the group would attack "the regime's strongholds in the heart of Damascus every time that surrounded civilians are targeted in Eastern Ghouta".

In other comments on all4Syria website, he identified three recent targets: the presidential palace, military and security buildings at Kafar Susah and Al-Mazzeh in the west of the city.

"We said in a statement that civilians should leave," the Ajnad al-Sham official said.

- Katyusha rockets -

On Tuesday night, at least 16 people including two children, were killed and 79 others wounded in rebel bombardments of several Damascus neighbourhoods, the Observatory said.

A resident of Qabun district, near the Jobar front line, said: "Ajnad al-Sham now has Katyusha rockets."

The man, who asked not to be named, said that on Tuesday he heard a rocket being launched from Jobar and his friend, speaking on the telephone, heard it fall in Malki.

Bombardment of rebel positions around Damascus resumed on Thursday. The rebels replied by firing mortars towards Abbassids Square near Jobar, the rebels and state news agency SANA said.

The Observatory estimates more than 170,000 people have died in the Syrian conflict which broke out in March 2011.