Syria has begun mixing chemicals that can be used to make deadly sarin gas, a U.S. official told AFP Monday, amid fears that President Bashar Assad's forces could attack rebels with chemical weapons.

"We've picked up several indications which lead us to believe that they're combining chemical precursors," the official said, on condition of anonymity, adding that the operation was apparently aimed at making sarin.

The European Union has decided to reduce its Syrian delegation because of security fears, the spokesman for the bloc's diplomatic chief said Monday, amid new fears chemical weapons could be used in the ongoing conflict.

"The EU delegation has decided to reduce activities in Damascus to a minimum level due to the current security conditions," spokesman Michael Mann said in a statement, after the United Nations announced it was indefinitely suspending operations in Syria and withdrawing non-essential staff.

The United Nations on Monday suspended operations in Syria and starting withdrawing non-essential staff because of the growing danger from the country's civil war, the U.N. spokesman said.

The United Nations will "suspend its missions within the country until further notice," U.N. spokesman Martin Nesirky told reporters.

Syrian foreign ministry spokesman Jihad al-Maqdessi has defected from President Bashar Assad's regime, a Syrian opposition leader announced on Monday.

“Maqdessi left Damascus for Beirut and from there he headed to an unknown destination,” Jamal al-Wadi, the director of the office of revolutionary movement of the Syrian National Council, told Sky News Arabia television.

Prime Minister Najib Miqati asked the Red Cross on Monday to mediate with Syrian authorities to retrieve the bodies of Lebanese Islamist fighters killed on Friday in the province of Homs, as the situation remained tense in the northern city of Tripoli.

In a phone conversation with the head of the International Committee of the Red Cross delegation in Lebanon George Montani, Miqati also urged the international organization to gather information about the other surviving fighters in the Syrian city.

Syrian President Bashar Assad's regime is in danger of collapse "anytime" as the opposition gains ground on the military and political fronts, Arab League chief Nabil al-Arabi said on Monday.

"That could happen anytime," the secretary general said in an interview with Agence France Presse.

Prime Minister Najib Miqati stated on Monday that tackling the case of Syrian refugees in Lebanon has become a “very pressing” issue.

He said: “Lebanon can no longer support their burden alone.”

For half a century Syria's filmmakers were forced to work under a numbing state censor or choose exile. But a flow of images beamed online from the conflict zone, spotlighted in Paris this week, may contain the seeds of a new Syrian cinema.

The French capital's Forum des Images film center is showcasing some of the gems to have slipped past the censors since the 1970s, alongside raw and urgent images born of the revolution.

U.S. Secretary of State Hillary Clinton on Monday issued a "strong warning" to the regime of Bashar Assad over the potential use of chemical weapons against the Syrian people.

"This is a red line for the United States," Clinton said after meeting Czech Foreign Minister Karel Schwarzenberg in Prague.

The Syrian army bombarded southern districts of the capital and suburbs overnight as part of an assault aimed at driving rebels out of footholds around Damascus, a monitoring group said on Monday.

The Syrian Observatory for Human Rights said artillery gunners targeted the districts of Hajar al-Aswad and Tadamun as well as the Palestinian refugee camp of Yarmuk in southern Damascus.