Washington/Beirut: The United States called on Wednesday for a new ceasefire in Syria as rival forces clashed in the country's northwest, where the government is waging an offensive on the last big stretch of rebel-held territory.
Syrian President Bashar al-Assad launched his assault late last month saying rebels had breached an existing ceasefire, triggering a civilian exodus by bombarding Idlib and adjacent areas.
Washington has said it sees signs that Assad has used poison gas in the latest offensive. He has denied such allegations throughout the war.
"What we really need in Idlib and throughout the country is a ceasefire," said James Jeffrey, the U.S. special representative for Syria.
"We are very much engaged in trying to get this stopped," he added in a House of Representatives committee hearing.
However, fighting raged on Wednesday as rebels sought to roll back army advances in the face of a heavy bombardment, state media, insurgents and a war monitor said.
Weeks of airstrikes, shelling and fighting have driven at least 180,000 people from their homes, raising fears of a new humanitarian disaster.
Many displaced people, camping on the Turkish border, voiced anger and frustration that Ankara had not done more to help them.
"We can no longer put up with living under bombardment or in the open under the trees," said Abu Abdullah, one of thousands of Syrians in white tents dotted around the rock-strewn olive groves close to the frontier.
Turkey-backed rebels had sent reinforcements on Saturday to the front lines of the insurgent enclave, which is dominated by the jihadist Tahrir al-Sham group, the latest incarnation of the former al Qaeda affiliate Nusra Front.
The war monitor, the Britain-based Syrian Observatory for Human Rights, said at least 100 air strikes hit rebel-held northwest Syria on Wednesday.
Syrian state media reported that the army had stopped a large attack by rebel groups in several places, killing many insurgents.
Rebels said they had recaptured the small town of Kafr Nabuda, which the government said it had taken early this month.
"There are a large number ...killed from Assad's forces... there are many bodies still on the ground in the town," said Naji Mustafa, a spokesman for the Turkey-backed National Liberation Front.
Assad has been backed during the eight-year war by Tehran and Moscow, and the Russian defence ministry said the Syrian army had repelled three big attacks on Wednesday by 500 fighters with seven tanks and about 30 trucks mounted with machine guns.
A truce was agreed in the northwest last year under a Russian-Turkish deal to avert a major government assault. However, Russia has voiced increasing frustration with what it calls violations of the agreement.
Turkish army posts were established along the front line last year to monitor compliance with the agreement. Turkish Defence Minister Hulusi Akar said on Tuesday they would remain, despite reports in Turkish state media that the Syrian army had carried out attacks near one of them.
The US State Department on Tuesday said it saw signs that the Syrian government may be using chemical weapons, including an alleged chlorine attack on Sunday. The French foreign ministry said the new allegations must be looked into.
Mustafa said the army had used chlorine gas when shelling Kubayna, in the mountainous frontline area in the northwest of the rebel enclave, causing choking symptoms among some fighters who were treated at a field hospital.
However, he said that because of the intense bombardment, they had not properly documented the cases.
Italy said on Wednesday that an Italian man held for three years in Syria had been freed.