The United States accused the Syrian government of using "new horrific tactics" on Monday, as UN observers reported Syrian helicopters were firing on rebellious areas and concerns mounted that civilians were trapped in besieged cities.

Activists reported more than 50 people killed across Syria on Monday, with violence in Homs, Idlib and Latakia provinces. According to activists' accounts, Syrian troops with helicopter gunships attacked Rastan, a rebel-held town in Homs province.

Rastan has resisted repeated government offensives for months. The death toll and the online videos were impossible to independently verify.

According to videos posted online, fireballs of orange flame and black rubble exploded in the air as waves of shells pounded residential buildings in Homs on Monday. The sounds of shells whooshed through the sky and there was occasional sporadic machine gun fire.

US State Department spokeswoman Victoria Nuland expressed concern about reports the regime "may be organizing another massacre'' in Latakia province, where UN monitors have been impeded from accessing.

[Source: AP]