Syrian activists say more than 300 people were killed across Syria on Thursday, in what is believed to be the deadliest day in the 16-month uprising against President Bashar al-Assad.

The London-based Syrian Observatory for Human Rights said Friday that nearly 100 of the people killed in the violence were government troops. Many civilians were also killed.

Also Friday, Syrian state media say government troops have recovered full control of a volatile neighborhood in Damascus, the Midan District.

Meanwhile, Russia has rejected Western criticism of its veto Thursday of a U.N. Security Council resolution that would have threatened Syria with sanctions if it does not halt violence.

China also vetoed the resolution, which would have extended the U.N. monitoring mission in Syria. The mandate of the mission is due to expire Friday. Council members are expected to meet again to consider a resolution that would extend the mandate for a brief period.

In another development, rebels seized control of major border posts with Iraq and Turkey, leading Iraqi officials to close off the border with Syria.