US Secretary of State John Kerry called Sunday for Syrian allies Russia and Iran to exert influence on the government of Bashar al-Assad to uphold a partial ceasefire that went into effect on February 27 and has since been holding, despite some breaches.
"The Syrian people support the cessation because it has made their lives better. The single biggest violator of that, by allegation, is the Assad regime," Kerry said of the "cessation of hostilities" deal brokered by the United States and Russia.
Kerry was speaking in Paris after a meeting with French Foreign Minister Jean-Marc Ayrault, counterparts from Britain, Germany and Italy and the EU's foreign policy chief.
"It is important for those who support the Assad regime to make sure it is living up to its commitments," Kerry said, responding to Syrian Foreign Minister Walid al-Moallem's comments Saturday rejecting diplomatic efforts to press for elections.
UN special envoy on Syria Staffan de Mistura recently said that presidential and parliamentary polls should take place in 18 months.
Kerry also hailed progress in the fight against Islamic State, saying the extremist group had lost 3,000 square kilometres and 600 fighters in the last three weeks alone.
He said the violence in Syria has decreased by 80 to 90 per cent, but issued a stark warning against allegations of further bombardment by the regime.
"If the regime and its backers think that they can test the boundaries, diminish compliance in certain areas, or act in ways that call into question their commitment to the cessation without serious consequences for the progress that we have made, they are deeply mistaken," Kerry said.
Delegates from al-Assad's government and the opposition are expected to participate in indirect peace talks in Geneva under UN auspices on Monday.
In February, de Mistura put the talks on hold amid an upsurge of violence in the country.
The truce, which has made the talks possible again, excludes Islamic State and al-Qaeda's Syria branch, the al-Nusra Front, meaning their forces can be targeted by airstrikes mounted separately by Russia and a US-led military alliance.
A monitoring group said Sunday that al-Nusra has overrun bases of a rival US-backed rebel group and detained dozens of its members with the help of allied militants.
Fighters from al-Nusra and the Soldiers of al-Aqsa militia took control of the premises of the moderate rebel group Division 13 in the north-western province of Idlib after overnight clashes, the Syrian Observatory for Human Rights said.
At least six fighters, including four from Division 13, were reportedly killed.
The jihadists also detained at least 40 members from Division 13, a subsidiary of the Western-backed opposition Free Syrian Army, according to the Britain-based watchdog.
After capturing the Division 13 bases in the town of Maaret al-Numan, al-Nusra hardliners seized weapons, including US-made anti-tank missiles and armoured vehicles, the Observatory said.