Iran will respond to any Israeli or U.S. attack against its nuclear sites with a "proportionate" reaction, the military adviser to the country's supreme leader Ali Khamenei said on Saturday.

General Yahya Rahim Safavi, quoted by Fars news agency, said however that such an attack was unlikely.

The head of Syria's largest exile opposition group said Saturday he would welcome Arab military action aimed at ending attacks by Bashar Assad's regime against Syrian rebel forces and civilians.

Burhan Ghalioun, head of the Syrian National Council, made the comments before a meeting of Arab League foreign ministers in Doha.

Arab leaders called for U.N. action on Saturday as at least 27 people were killed in Syria amid growing concern that Kofi Annan's peace plan is failing and the country descending into all-out civil war.

Annan himself warned of sectarian warfare, singling out Syrian President Bashar Assad and his regime as key to resolving the conflict.

Syrian troops conducted raids in search of anti-regime militants and clashed with rebels on Saturday in several regions of the country, with at least 39 people killed including 22 soldiers, a policeman, 15 civilians and one deserter, the Syrian Observatory for Human Rights said.

In central Homs province, one civilian was killed during raids of the town of Karatin, and a man and his daughter were fatally shot on a bus on the road to Talbisseh.

Arab League Secretary General Nabil al-Arabi said on Saturday he has asked the U.N. Security Council to take strong action in order to protect civilians in Syria.

"I sent a letter to the U.N. Security Council asking it to undertake all necessary measures to protect the Syrian people," Arabi told Agence France Presse shortly before the opening of a meeting of the ministerial committee on the Syrian crisis.

French President Francois Hollande said Friday that no solution is possible in Syria without "the departure of Bashar Assad.”

He spoke at a press conference with Russia's Vladimir Putin.

A judge sentenced former Egyptian president Hosni Mubarak to life in prison on Saturday after convicting him of involvement in the murder of protesters during the uprising that ousted him last year.

A senior lawyer for Mubarak's defence team told Agence France Presse the strongman, who was taken to a Cairo prison after the hearing, will appeal the sentence.

The United Nations said Friday the Syrian government has released 223 prisoners, but stressed that many more must still be freed.

U.N. monitors on Thursday saw 210 detainees released in Damascus and 13 in the southern city of Daraa, U.N. deputy spokesman Eduardo del Buey said.

The rebel Free Syrian Army on Friday announced it was resuming "defensive operations" after the expiry of its ultimatum for the regime to respect international envoy Kofi Annan's six-point peace plan.

"We will now resume defensive operations," FSA spokesman Qassem Saadeddine told Agence France Presse via Skype. "We will not go on the offensive because we do not want to be singled out as the ones responsible for breaking the peace initiative."

Russia's foreign ministry on Friday blamed the Houla massacre, in which 108 people were killed, on foreign assistance to Syrian rebels, including arms deliveries and mercenary training.

"The tragedy in Houla showed what can be the outcome of financial aid and smuggling of modern weapons to rebels, recruitment of foreign mercenaries and flirting with various sorts of extremists," the ministry said in a statement.