BEIRUT: Syria on Monday rebuffed an Arab League call for President Bashar Assad step down in favor of a unity government as interference in its affairs, underlining its determination to defeat a 10-month-old uprising seeking Assad's overthrow.

It was not immediately clear whether Syria would accept the League's decision to keep Arab observers in the country for another month despite their failure to stem bloodshed in which hundreds of people have died since they deployed on Dec. 26.

But any credibility the mission might retain was undermined when Saudi Arabia, a foe of Syria's closest ally Iran, announced it would withdraw its own monitors because of the Syrian authorities' failure to cooperate with its mandate. It was unclear if other Gulf states would follow suit.

An official Syrian source quoted by the state news agency SANA said the new Arab League plan, which told Assad to hand power to a deputy pending democratic elections, reflected a "conspiracy against Syria".

"Syria rejects the decisions of the Arab League ministerial council ... and considers them a violation of its national sovereignty and a flagrant interference in its internal affairs," the source said.

Rami Khouri, a Beirut-based commentator, said the unusually bold Arab plan announced at the Arab League's Cairo headquarters on Sunday was clearly "bad news" for Assad.

"The fact that Arab countries would propose such a clear intervention and essentially order him to step aside and give him a mechanism to do so is quite a dramatic sign of how much credibility and legitimacy he has lost in the region," he said.

Assad, 46, has faced more than 10 months of protests against his rule and a growing armed rebellion. The United Nations says 5,000 people have been killed in the security crackdown. The authorities say they are fighting foreign-backed armed "terrorists" who have killed 2,000 soldiers and police.

Saudi Foreign Minister Saud al-Faisal, referring to an Arab League plan accepted by Damascus in November, said Riyadh would withdraw its monitors "because the Syrian government did not execute any of the elements of the Arab resolution plan".

That earlier plan demanded that Assad end violence, withdraw troops from urban areas, free detainees, allow peaceful protests and engage in dialogue with the opposition.

"We are calling on the international community to bear its responsibility, and that includes our brothers in Islamic states and our friends in Russia, China, Europe and the United States," Faisal said, calling for "all possible pressure" on Syria.

The Syrian official source upbraided Arab ministers for making inflammatory remarks instead of denying money and weapons to "terrorist groups" in Syria and criticized the League for ignoring Assad's promised reforms, which were lacking "in many of the Arab states leading the hostile campaign against Syria".

Splits among the League's 22 members have complicated its diplomacy on Syria, but in the end only Lebanon refused to approve Sunday's proposal, although Algeria objected to taking the plan to the United Nations Security Council.

The main opposition Syrian National Council (SNC), which has urged the League for weeks to refer the Syria crisis to the Security Council, welcomed the initiative.

"This confirms that all Arab countries today consider the tyrannical regime of Bashar Assad to be finished and that it must be replaced," SNC chief Burhan Ghalioun said in Cairo.

The Security Council is also divided on how to respond, with Western powers demanding tougher sanctions and an arms embargo, measures opposed by Assad's ally Russia.

Asked about previously announced Arab sanctions on Syria, Qatari Prime Minister Sheikh Hamad bin Jassim al-Thani said: "Arab economic sanctions will be imposed via the Security Council." He did not elaborate.

Qatar said it was time to rethink the observer mission to Syria and consider sending Arab peacekeepers.

"The reality says that the bloodshed has not stopped and the killing machine is still working and violence has spread everywhere," Sheikh Hamad told his Arab colleagues.

Syria, keen to avoid tougher foreign action, has tried to show it is complying with the initial Arab peace plan.

This month the authorities freed hundreds of detainees, announced an amnesty, struck a ceasefire deal with rebels in one town, allowed observers into some trouble spots and admitted some foreign journalists. Assad also renewed his pledges of reform.

SANA, the state news agency, said 5,255 prisoners had been released under an amnesty announced by Assad a week ago for offenses committed since the uprising began in March.

The violence, however, has raged on unabated.

SANA said Brigadier-General Hassan al-Ibrahim, a specialist in "electronic warfare management", and another officer were killed on Sunday when insurgents shot at their car in Damascus province. He was the third brigadier killed in a week.

It said 11 people were also killed when attackers fired guns and rocket-propelled grenades at a civilian bus in the Ashira district of Homs, a rebellious central city.

The opposition Syrian Observatory for Human Rights said Sunday's civilian death toll stood at 12, nine of them in the towns and villages of Damascus province.