Damascus said on Wednesday it will stop cooperating with international peace envoy Lakhdar Brahimi unless he severs his ties with the Arab League, which it accused of involvement in a conspiracy against Syria.
"Syria has cooperated and will cooperate with Brahimi only as UN envoy, because the Arab League is complicit in the conspiracy against Syria," the foreign ministry said in a statement carried by state media.
It lashed out at the UN-Arab League envoy and said there was "a lack of neutrality" in his work.
Brahimi was named to the joint post in August to replace former UN chief Kofi Annan, who stepped down after failing to get the two sides to implement a peace plan he had proposed.
Last month, the Arab League granted the Syrian seat to the main opposition National Coalition, in a move that sparked rage from Damascus.
"Brahimi's report (on April 19) to the UN Security Council was marked by (a tone of) interference in Syria's internal affairs and a lack of the neutrality required by his mission as international mediator," the statement said.
Brahimi told the council that Syrian President Bashar al-Assad is "not in the mood for dialogue."
The veteran Algerian diplomat also urged the council last Friday to impose an arms embargo on all sides of the Syrian conflict, a senior UN official said on Wednesday.
"If Brahimi wants his mission to succeed, we expect Brahimi to start working to stop the violence and terrorism along with the parties concerned, and to expose the roles played by France, Britain, Turkey, Qatar and Saudi Arabia, which finance and arm Al-Nusra Front's terrorists," said the ministry.
Al-Nusra is a jihadist movement that has seized an increasingly important role in the two-year-old uprising to unseat Assad.
Ever since the start of the revolt in March 2011, Damascus has systematically described rebels as foreign-backed "terrorists."