U.N. weapons inspectors were shot at while travelling on Monday to sites near Damascus where chemical weapons were allegedly used and over which the West has warned of consequences for the regime of President Bashar al-Assad.

The first vehicle of the Chemical Weapons Investigation Team was “deliberately shot at multiple times” by unidentified snipers, the U.N. said.

As the car was no longer serviceable, the team returned safely back to a government checkpoint. Inspectors will return to the area after replacing the vehicle, it added.

A U.N. source said that the team was near the town of Maadamiyet al-Sham, south-west of Damascus.

The town is one of two main sites where the opposition claims the government used a poisonous gas on August 21, leaving 1,300 people dead. The government has vehemently denied the charge.

Western nations have warned that the use of chemical weapons would be a trigger that could result in an armed reaction.

French President Francois Hollande said that the U.S. and its allies would decide within days on a response.

“Everything will play out this week,” Mr. Hollande told Le Parisien newspaper, echoing the remarks of Foreign Minister Laurent Fabius who spoke earlier of a reaction “in the coming days.” “There are several options on the table that ranges from the reinforcement of international sanctions to air strikes to arming the rebels,” Mr. Hollande said.

“We will also leave a little time for the diplomatic process, but not too much time. We cannot not react to the use of chemical weapons,” he said.

Germany warned that there would be “consequences” as Chancellor Angela Merkel called for “a clear and united” international response.

British Prime Minister David Cameron is cutting his holiday short to return to London to chair a meeting of the National Security Council in which potential military action against will be discussed on Tuesday.

A report in The Times newspaper said the British and American Army chiefs would meet on Monday. A single bombardment of government positions from ships was the favoured approach, it said.

The United States said it was weighing its options and preparing for “all contingencies.” A NATO official speaking on condition of anonymity said that if poisonous gas was in fact used by the Syrian regime, it would be “completely unacceptable” and “a clear breach of international law.” However, Syria allies Russia and Iran warned the U.S. over the dangers of foreign incursions.

Russian Foreign Minister Sergei Lavrov in a telephone call with U.S. Secretary of State John Kerry urged Washington “not to succumb to provocations” but to ensure that U.N. weapons inspectors can carry out an objective investigation, the Foreign Ministry in Moscow said.

Mr. Lavov also told Mr. Kerry that the U.S. should not heed reports about the attack near Damascus because the incident was most likely staged.

He warned that U.S. intervention in Syria would “annihilate” the joint Russian-American efforts to help achieve peace.

The al-Assad regime has rejected the allegations and accused the rebels of using chemical weapons.

“This is nonsense: First make accusations, and only then collect evidence. And this is being done by a powerful country - the United States,” Mr. Assad said in an interview with the Russian newspaper Izvestia.

A 20-member U.N. team, led by Swedish chemical weapons expert Ake Sellstrom, have been in Damascus since August 18, to investigate alleged use of chemical weapons.

In Amman, top western and Arab military leaders began deliberations reviewing “all options” regarding a response to the alleged attacks, including direct military strikes on Syria.

More than 100,000 people have been killed in Syria since an uprising against Assad’s rule started in March 2011, the U.N. says.

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