BEIRUT (TIP): Over 300 people were killed in Syria on Wednesday, the Syrian Observatory for Human Rights said, in one of the bloodiest days in the 18-month uprising against President Bashar al-Assad.

World leaders meeting at the UN have expressed concern at the continuing violence in Syria but are deadlocked over their response to the conflict, which the Observatory says has claimed 30,000 lives since March 2011.

The British-based organization, which monitors violence in Syria through a network of activists, said in a report released on Thursday that 55 people were killed in rural areas around Damascus. They included at least 40 who seemed to have been shot in al-Dhiyabia, southeast of the capital.