The United States, France and Britain warned President Bashar al-Assad yesterday that there would be consequences if he fails to stick to a deal under which Syria must give up its chemical weapons, and UN experts confirmed sarin gas was used in the August 21 attack in Damascus.

The three Western permanent members of the United Nations Security Council said they would seek a strong UN resolution setting binding deadlines for the removal of Syria’s chemical weapons, French President Francois Hollande’s office said.

Russia, which negotiated the deal with the US, cautioned against imposing tough penalties on the Syrian leader, who is Moscow’s close ally. In Syria, fighting was reported on several fronts, and Turkey said its warplanes shot down a Syrian helicopter after it violated Turkish airspace.

Turkey’s Deputy Prime Minister Bulent Arinc told reporters in Ankara after a regular Cabinet meeting: “Today at 1420 an Mi-17 helicopter belonging to Syria violated the Turkish border in the Guvecci area of Yayladagi in Hatay province by two kilometres.”

“It was repeatedly warned by our air defence elements. When the violation continued, our planes... hit the helicopter at 1425 with a missile causing it to fall on Syrian soil.”

Meanwhile a UN report on the August 21 attack confirmed “unequivocally and objectively” that chemical weapons were used, according to UN Secretary General Ban Ki-moon.

“This is a war crime,” Ban told the Security Council. “The international community has a responsibility to hold the perpetrators accountable and to ensure that chemical weapons never re-emerge as an instrument of warfare.” As expected, the report did not say who carried out the attack. Ban said on Friday that Assad “has committed many crimes against humanity,” although he did not ascribe blame for this specific incident.

Assad and Moscow have blamed the rebels.

The US reached a deal at the weekend with Russia that could avert US strikes on Syria as punishment for last month’s attack.

US Secretary of State John Kerry told a news conference in Paris that the three powers agreed with Russia that Assad must suffer consequences if he fails to comply with UN demands.

“If Assad fails in time to abide by the terms of this framework, make no mistake, we are all agreed – and that includes Russia – that there will be consequences,” Kerry said.

The accord offered the Syrian leader “no lifeline” and he had “lost all legitimacy”, Kerry added.

After Hollande met Kerry and British Foreign Secretary William Hague and their French counterpart Laurent Fabius, an aide to Hollande said: “The idea is to stick to a firm line”.

“They’ve agreed to seek a strong and robust resolution that sets precise and binding deadlines with a calendar,” said the official, who spoke on condition of anonymity.

Russia accused the Europeans of trying to reinterpret the agreement.

Speaking in Moscow, Foreign Minister Sergei Lavrov said any rush to draw up a resolution threatening to punish Syria in the event of non-compliance showed a “lack of understanding” of the agreement reached for Assad to give up his chemical weapons.

“Our (European) partners want to again unilaterally review what we’ve agreed on with the Americans. That’s not how you do business, and I’m sure that despite these statements that are coming from European capitals, the Americans will, as proper negotiators, strictly stick to what has been agreed on,” Lavrov said.

He also said it may be time to consider efforts to force the opposition to attend an international peace conference instead of just urging them to do so. So far, the rebels have said they will not attend talks if the Syrian president is there too.

The deal reached in Geneva put off the immediate threat of air strikes, and Lavrov stressed at the time that it did not include any automatic use of force in the event of Syria’s failure to comply.

But President Barack Obama has said force remains an option if Assad reneges.

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