Syrian rebels have said they are under fierce government attacks near the Turkish border despite a cessation of hostilities agreement as the United States expressed concern about regime assaults on civilian areas.
The agreement drawn up by the US and Russia, which came into effect on Saturday, has slowed but not entirely stopped fighting in the conflict approaching its sixth anniversary. Both the Syrian government and rebels have accused each other of violations.
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The Reuters news agency quoted a rebel official and the Britain-based Syrian Observatory for Human Rights monitoring group as saying that government forces pressed an offensive against opposition forces in Latakia province at the Turkish border on Wednesday.
Fadi Ahmad, spokesman for the First Coastal Division, a Free Syrian Army group, said government forces had brought in reinforcements and that fighting was as intense as anything preceding the cessation of hostilities.
"The battles were today very fierce," he told Reuters.
The Syrian government has prioritised securing the Turkish border through which rebel groups are supplied with weapons from states seeking Syrian President Bashar al-Assad's downfall.
The area being fought over in Latakia overlooks the rebel-held town of Jisr al-Shughour in neighbouring Idlib province, and the Ghab Plain, where rebel advances last year were seen as a growing threat to Assad, Reuters reported.
"Battles continue in vital areas that the regime wants, and where there was no truce in the first place. There is bombardment and battles," a rebel commander told Reuters.
"We are in the fifth day and there is no change in these areas," he said, in reference to areas in the provinces of Latakia, Homs and Hama.
There was no immediate comment from Damascus, which has denied breaching the terms of the truce.
Meanwhile, the White House said it had seen a reduction in air strikes against the opposition and civilians in Syria in recent days but was concerned by reported tank and artillery attacks.
"We are concerned about reports that the Syrian regime has engaged in tank and artillery attacks against civilians," White House spokesman Josh Earnest said, referring to reports about strikes near Latakia.
"Obviously those kinds of attacks - if confirmed - would be a flagrant violation of cessation of hostilities."
The United Nations said on Tuesday that peace talks between the warring parties in the Syrian conflict were scheduled to begin on March 9 in Geneva, urging them to ensure the cessation agreement take hold to allow them to come to the table.
But opposition official George Sabra said on Wednesday the dates for a resumption of talks remained "hypothetical" as long as the current truce did not fulfill humanitarian demands.
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"As long as the truce does not help implement the terms [of a UN resolution], all dates for the resumption of negotiations remain hypothetical," Sabra told Arabic news channel Arabiya al-Hadath on Wednesday.
The opposition is pressing for full humanitarian access to rebel-held areas and for detainees to be released - terms set out in a UN Security Council resolution passed in December.
"What is the value of a truce if its overseers - meaning US and Russia - do not push all sides to abide by it?" Sabra said.
The agreed agreement does not include the Islamic State of Iraq and the Levant (ISIL) or al-Nusra Front groups, which are recognised as "terrorist groups" by the UN.