France on Tuesday joined the United States and NATO in delivering a blunt warning to Damascus not to use chemical weapons on rebels, warning that the international community would react if it did.

"Any use of these chemical weapons by (Syrian President Bashar) Assad would be unacceptable," foreign ministry spokesman Vincent Floreani told reporters.

Activity around Syria's chemical weapons is ringing alarm bells in Washington and other world capitals, but secrecy surrounding the stockpile makes it difficult to gauge its nature and size.

U.S. President Barack Obama on Monday warned Syrian President Bashar Assad "there will be consequences" if he unleashed those weapons in the civil war wracking his country.

A rebel mortar attack on a school in a camp for displaced people near Damascus on Tuesday killed nine students and their teacher, Syrian state television reported, branding it a "horrific crime."

The broadcaster also reported 20 people were injured in the attack, but it was not immediately possible to verify their identities.

Any use by the Syrian regime of chemical weapons against its own people would spark an immediate reaction by the international community, NATO head Anders Fogh Rasmussen warned Tuesday.

"The possible use of chemical weapons would be completely unacceptable to the whole international community and and I would expect an immediate reaction from the international community," Rasmussen said.

The Syrian army shelled several areas east and southwest of Damascus early Tuesday hours after radical Islamist fighters seized a village in an eastern province bordering Iraq, a watchdog said.

"The army shelled the orchards in the Eastern Ghuta region (east of the capital), as it pressed on with its military campaign in the area," said the Britain-based Syrian Observatory for Human Rights.

Saudi Arabia's foreign minister urged on Tuesday the international community to have a unified position over Syria after the war-torn country's opposition formed a coalition last month.

"We see in forming the new Syrian coalition an important positive step towards uniting the opposition under one banner," Prince Saud al-Faisal told reporters.

Germany warned Syria Tuesday against any use of chemical weapons, ahead of a NATO meeting on Turkey's request for deployment of Patriot missiles to counter a potential threat from its neighbor.

"I can only warn the Syrian regime: a use of chemical weapons would be totally unacceptable," German Foreign Minister Guido Westerwelle said ahead of the gathering of his NATO counterparts in Brussels.

General Prosecutor Judge Hatem Madi tasked on Tuesday the Central Criminal Investigations Bureau with examining audio recordings implicating al-Mustaqbal MP Oqab Saqr in the transfer of arms to Syria.

The state-run National News Agency said that Madi tasked the bureau with studying the audio recordings of Saqr to take the necessary decisions in light of the Lebanese regulations and the bilateral treaties with the Syrian government.

Syrian rebel fighters on Monday shot down a MiG warplane in Damascus province that had been bombing rebel strongholds, activists said.

Details of the incident were scarce and there was no immediate confirmation from the Syrian authorities.

President Barack Obama dramatically told Syria's President Bashar Assad Monday not to turn chemical weapons on his own people, following U.S. warnings his forces were mixing deadly sarin gas.

Obama publicly told the increasingly isolated Assad not to unleash the "worst weapons of the 20th century" in the 21st, capping a day of alarming American warnings on the Syrian regime's intentions.