The UN Secretary-General Ban Ki-Moon has urged the Syrian government to allow UN observers to enter the town of Haffa in Latakia Province citing "reports of a build-up of government forces around the town".
A statement from his office also said: "The government's intensive military operations, including the shelling of Homs and reportedly other population centers, as well as firing from helicopters on Talbiseh and Rastan, are resulting in heavy civilian casualties and human rights violations."
The United States and Russia are embroiled in a furious diplomatic row after both sides accused each other of supplying arms to Syria.
The US Secretary of State has accused Russia of escalating the conflict in Syria and lying about their involvement in the country.
Foreign Secretary William Hague has told MPs in the House of Commons that Syria is "on the edge of civil war."