Syria's opposition urged the world to unite in action against Syrian President Bashar Assad Friday, following the carnage in village of Tremseh, which left over 220 dead. International mediator Kofi Annan said Friday that Syrian forces had used heavy weaponry against Treimsa, in the Hama region, in violation of its commitments to his peace plan. Related stories: US fears Assad relocating chemical stockpiles Russia drafts resolution to extend UN Syria mission Activists: Over 200 dead in Syria massacre In a statement condemning the atrocities, Annan voiced shock at the "intense fighting, significant casualties, and the confirmed use of heavy weaponry such as artillery, tanks and helicopters." Massacre in Hama region Meanwhile, UN observers in Syria are ready to go to the central of Tremseh, if a ceasefire will be put in place, mission chief Major General Robert Mood said. "UNSMIS stands ready to go in and seek verification of facts if and when there is a credible ceasefire," he said. Survivors of the Tremseh massacre and activists recounted the horrors, telling of how "gunmen went from house to house clinically executing survivors," while others were shot dead as they tried to escape through the fields surrounding the village. Syria state television made no mention of the massacre, reporting only of "terrorist action" against Assad's troops. The Syrian government said that only 50 people died in the village, saying that "the killing was carried out by rebels and foreign journalists." "The bloodthirsty media in collaboration with gangs of armed terrorists massacred residents of Tremseh village… to sway public opinion against Syria and its people and provoke international intervention on the eve of a UN Security Council meeting," state-run news agency SANA said. Reuters and news agencies contributed to this report Follow Ynetnews on Facebook and Twitter Receive Ynetnews updates directly to your desktop