The latest flare-up of violence came as Kofi Annan, the UN-Arab League envoy to Syria who brokered a repeatedly-violated ceasefire last month, finalised plans to return to Damascus.
Diplomats in Geneva said the former UN secretary general would visit the Syrian capital early next week.
A report by current UN leader Ban Ki-moon said meanwhile that groups fighting president Bashar al-Assad now control “significant” parts of some cities and there is “considerable physical destruction” across the country.
“There is a continuing crisis on the ground, characterized by regular violence, deteriorating humanitarian conditions, human rights violations and continued political confrontation,” said the report, obtained on Friday.
It is to be debated by the UN Security Council next week.
More than 50 civilians, including 13 children, were killed in army shelling of Houla, a town in the central province of Homs, the Syrian Observatory for Human Rights said.
“It was a real massacre that took place and the UN observers are just staying silent,” the head of the monitoring group, Rami Abdel Rahman, said in a telephone call.
For the first time since the uprising against Mr al-Assad’s regime erupted 14 months ago, army tanks rumbled through Aleppo, said the Britain-based watchdog.
It also said helicopter gunships went into action against rebels, strafing mountain villages in the Latakia area of north-western Syria, near the Turkish border, wounding at least 20 people.
At least four policemen were killed in clashes with rebels in Kansebba, in the same area, the Observatory added.
Hours after massive anti-regime rallies across Aleppo, tanks deployed in the city, Syria’s economic hub, rumbling through the Kalasse and Bustan al-Kasr neighbourhoods after thousands attended a funeral, it said.
Earlier the group reported that a young man was killed in Aleppo when troops fired with live rounds and tear gas on protesters in the city, where 12 massive anti-regime rallies took place on Friday.
Another four civilians were also killed by gunfire in Aleppo, the rights watchdog added, including two children.
In all more than 70 people were killed on Friday, according to an Observatory tally, including 10 in Hama province, also central Syria.
A UN panel said on Thursday that government forces were to blame for most abuses in the violence that has raged on daily despite the ceasefire supposed to take effect April 12.
Mr Annan, who brokered the six-point peace plan, is to travel to Syria “soon” as he continues efforts to find a peaceful solution to the crisis, his spokesman Ahmad Fawzi said.
Source: ABC News