Syrian rights activists say government troops have attacked the southern city of Daraa, the place where an opposition uprising against President Bashar al-Assad's rule began last March.

The Britain-based Syrian Observatory for Human Rights says four people were killed there Thursday, including fighting between Syrian forces and rebel soldiers.

China said Thursday it is sending a senior diplomat to Syria for talks about the crisis. Foreign Ministry spokesman Liu Weimin said Vice Foreign Minister Zhai Jun will be in Syria on Friday and Saturday, but could not say who will be involved in the talks.

“The specific timetable of the event is still being organized. I want to send a message that China hopes to push forward a peaceful and appropriate resolution to the Syria crisis. China is willing to continue playing a constructive mediation role in resolving the crisis.”

He said China wants to press for a peaceful resolution. The vice foreign minister met with a Syrian opposition delegation last week in Beijing.

Meanwhile, the U.N. General Assembly is expected to give broad support Thursday to a resolution accusing Syria of rights violations and calling on the government to stop its deadly crackdown on dissent. The document circulated by Arab diplomats is non-binding.

Russia and China vetoed a U.N. Security Council resolution earlier this month, blocking the body from endorsing a Western- and Arab-backed plan for President Assad to step aside as a way of ending the crisis.

The vote comes a day after Mr. Assad ordered a constitutional referendum that he said would end nearly five decades of single-party rule.

The proposed charter, set for a February 26 vote, would dilute the ruling Ba'ath party's status as “the leader of the state and society.” State media said Wednesday the draft also permits a president to be elected to two seven-year terms, setting a limit for the first time in decades.

Mr. Assad's late father, Hafez al-Assad, ruled for 29 years before his death in 2000, when his son succeeded him. The Ba'ath party took power in 1963.

Russia welcomed the proposed referendum, but Syrian opposition groups quickly rejected it, saying the government was stalling for time and that the Syrian people would accept nothing less than Mr. Assad's ouster. White House spokesman Jay Carney dismissed the referendum as “laughable,” saying it “makes a mockery” of the Syrian uprising.

Rights groups say more than 6,000 people have been killed since pro-Assad forces began cracking down on anti-government protesters last year. The United Nations stopped updating the death toll in January, saying it was too difficult to obtain information.