Syrian troops have shelled the southern city of Daraa, killing at least 17 people, activists said, while in Damascus, residents spoke about a night of shooting and explosions in the worst violence Syria's capital has seen since the uprising against President Bashar Assad's regime began 15 months ago.
The fighting in Damascus suggested a new boldness among armed rebels, who previously kept a low profile in the capital.
It also showed a willingness by the regime to unleash in the capital the sort of elevated force against restive neighbourhoods it has used to crush opponents elsewhere.
For the first time in the uprising, witnesses said, regime tanks opened fire in the city's streets, with shells slamming into residential buildings.
The latest escalations in different parts of Syria are another blow to international envoy Kofi Annan's peace plan, which aims to end the country's bloodletting. Annan brokered a ceasefire that went into effect on April 12 but has since been violated nearly every day since and never properly took hold.
UN observers in the country ostensibly to monitor the ceasefire issued the first independent video images from the scene of a reported massacre last week in a remote farming village. Activists say up to 78 people, including women and children, were shot, hacked and burned to death in Mazraat al-Qubair on Wednesday.
The video, taken in the UN visit a day earlier, showed blood splashed on a wall pockmarked with bullet holes and soaking a nearby mattress. A shell punched through one wall of a house. Another home was burnt on the inside with dried blood was splashed on floors.
After the observers' visit, UN spokeswoman Sausan Ghosheh said the scene held evidence of a "horrific crime" and that the team could smell the stench of burned corpses and saw body parts strewn around the now deserted village, once home to about 160 people.
She said residents' accounts of the mass killing were "conflicting," and that the team was still cross checking the names of the missing and dead with those supplied by nearby villagers.
Opposition activists and Syrian government officials blamed each other for the killings. Activists accused pro-government militiamen known as "shabiha". A government statement on the state-run news agency SANA said "an armed terrorist group" killed nine women and children before Hama authorities were called and killed the attackers.