The United Nations General Assembly votes Friday on a Saudi-drafted resolution on Syria, as activists report more violence in the 17-month uprising against President Bashar al-Assad.

The Britain-based Syrian Observatory for Human Rights said Friday that shelling of a Palestinian refugee camp in the capital, Damascus, Thursday killed at least 21 people. The Observatory did not say who fired the mortars.

The group also reported clashes and government attacks Friday in other areas of the country, including the provinces of Hama, Idlib and Aleppo.

The non-binding U.N. resolution would condemn both the Assad government's use of heavy weapons and the U.N. Security Council's failure to agree on measures to stop the violence.

The vote comes just one day after Kofi Annan announced his resignation as U.N. – Arab League envoy to Syria, blaming what he called a lack of unity in the Security Council.

The White House said Mr. Annan's resignation highlights the failure of Russia and China to back meaningful resolutions against Mr. Assad.

China said it regrets Mr. Annan's resignation and understands the difficulties of his mediation work. Chinese foreign ministry spokesman Hong Lei said China is open to initiatives that are conducive to a “political resolution” to the Syrian conflict. He said China supports the U.N. continuing to play an important role in an appropriate solution.

Both the Syrian rebels and the government failed to commit themselves to Mr. Annan's peace plan for Syria, which included an immediate cease-fire and talks on a transitional government. The three Security Council resolutions that China and Russia vetoed would have held President Assad responsible for his failure to abide by the Annan plan and threatened him with sanctions.