Syrian opposition groups will reject a political transition plan proposed by peace envoy Kofi Annan unless it explicitly requires President Bashar al-Assad to quit before a unity government is formed, a senior opposition official said on Thursday, June 28.

According to Reuters, diplomatic sources at the United Nations said Annan's proposal, aimed at ending the 16-month conflict in Syria, does not stipulate Assad's resignation although it does say the unity government could not include figures who jeopardize stability.

"The proposal is still murky to us but I can tell you that if it does not clearly state that Assad must step down, it will be unacceptable to us," said Samir Nashar, an executive member of the international Syrian National Council.

Annan's transition proposal is one of the main topics that Russia, the other four permanent UN Security Council members and key players in the Middle East will discuss at a meeting in Geneva on Saturday, according to United Nations diplomats.

To win UN backing the plan must have the support of Syria's powerful ally Russia, which has so far rebuffed Western attempts to force Assad to cede power as rank interference in the country's sovereignty.

For the opposition, Assad's departure is imperative.

"If the proposal said Assad must step down, then the idea of allowing other members of the current government to participate could be open to discussion," Nashar said.

But rebel fighters locked in the war to topple Assad said there was no part of the plan they could accept, and they had lost patience with UN envoy Annan's peace-making efforts.

"This is just a new labyrinth. It is new silliness for us to get lost in and haggle over who can participate and who can't," said Ahmed, a Free Syrian Army (FSA) fighter in Homs, epicenter of the revolt against four decades of Assad family rule in which the more than 10,000 people have been killed, by a UN count.