Syrian regime forces opened fire on protesters in the Douma area near the capital on Friday, activists said, as monitors reported that at least 13 people were killed in violence across the country.
Scores of protests broke out in towns and cities across Syria to condemn the May 25 Houla massacre.
At a protest in Douma, "regime forces opened fire on demonstrators. Everyone had to run away because there was nobody there to protect them," activist Mohammed al-Dumani said via Skype.
He said several people were wounded.
The demonstrations were called to commemorate the 108 victims of a massacre last week, including 49 children, in the central town of Houla. Activists hailed the children as the "flares of victory" in the 15-month anti-regime uprising.
Large crowds in Aleppo, northern Syria, "chanted for the victory of the martyrs of Houla," also reportedly coming under regime gunfire, another activist who declined to be named told AFP.
"People chanted in honour of the martyrs of Houla, and condemned the failure of (UN-Arab League envoy Kofi) Annan's peace plan," notably a ceasefire which has been violated each day, Halabi added.
The UN-backed ceasefire that came into force on April 12 has failed to take hold. According to the Syrian Observatory for Human Rights, almost 2,300 people have been killed since the start of the truce.
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The Observatory said two people were killed and a third seriously injured in an explosion in the Mazzeh neighbourhood of Damascus.
Earlier on Friday, regime troops killed five people during raids and shelling of rebel positions in the town of Daraya outside the capital, the Britain-based monitoring group said.
Regime troops stormed the town -- a centre for the armed opposition -- with tanks and fired shells at its western districts, the Observatory said.
The Houla massacre, which Damascus blamed on "armed groups," stoked an international outcry and the expulsion of top Syrian diplomats from several Western countries.
On Friday morning, in Al-Esseily neighbourhood of Damascus, protesters demanded that further action be taken against the Syrian authorities.
"O Arabs, we demand more than the expulsion of the (Syrian) ambassadors; we also demand the expulsion of the Russian and Chinese ambassadors" in Damascus, read one poster.
In the southern province of Daraa, a man was shot dead as he left a mosque in Al-Sheikh Maskeen village, while heavy gunfire and explosions were reported in several towns.
In the city of Homs, central Syria, regime forces shot dead four people, while a child was injured in shelling of Houla, in the province of the same name, according to the Observatory.
And regime forces in Deir Ezzor province of eastern Syria shot dead a civilian in the town of Bukamal, it said.