United Nations-Arab League peace envoy Lakhdar Brahimi is set to meet Friday in Geneva with U.S. and Russian officials to discuss finding a political solution to the conflict in Syria.

The United States is among members of the U.N. Security Council who back a political transition plan for Syria that includes Syrian President Bashar al-Assad stepping down from power. But Russia and China, both permanent members of the Security Council, oppose such a plan.

On Thursday, Syria accused Brahimi of “flagrant bias” in comments he made a day earlier insisting Mr. Assad must step down. U.S. State Department spokeswoman Victoria Nuland said Thursday that the United States strongly supports Brahimi's mission.

The Syrian ambassador to the U.N., Faysal Hamoui, told reporters Thursday in Geneva that Syria is not participating in the meeting and expects no results.

“Nothing, no, no. We are not linking, we don't have anything with this meeting. We will see, we will see.”

Meanwhile, reports from Syria indicate armed rebels have seized a portion of Taftanaz, Syria's main air base in the north. Nuland said such a development would be a “significant blow” to the Assad regime and added the reports indicate that the rebels are gaining strength.

Also Thursday, a group of 48 Iranians held hostage by Syrian rebels returned to Iran after being freed in a prisoner swap with President Assad's government.

The hostages, held for five months, were freed in exchange for 2,130 prisoners, mostly Syrian, in what appears to be the first major prisoner swap during the nearly two-year-old civil war.

The bloodshed in Syria has left more than 60,000 people dead since March 2011.