Russian President Vladimir Putin has told European leaders that Moscow is committed to a upholding a ceasefire that took hold in Syria last weekend, German Chancellor Angela Merkel said.

The leaders of France, Britain, Germany and Italy had a teleconference conversation with Putin on Friday, during which they asked him to use Russia's influence over the Syrian government to abide by the truce.

"I would like to stress one more time that the commitment to hold the ceasefire was confirmed as a key message by the Russian president: only attacks on Daesh [ISIL] and al-Nusra Front," Merkel said during a news conference with French President Francois Hollande.

Merkel was referring to US-Russia-backed plans for a "cessation of hostilities" in Syria that excludes groups such as the Islamic State of Iraq and Levant [ISIL] and al-Nusra Front.

The UN Security Council unanimously passed a vote on February 26 to support a pause in fighting in Syria, demanding that all parties to the agreement fulfill their commitments to end hostilities.

Syrian opposition coordinator Riad Hijab, however, said Syrian President Bashar al-Assad, Russia and their allies had carried out 90 air strikes in the country since the ceasefire was declared.

Speaking at a news conference in Paris, the former Syrian prime minister said that the conditions of the truce had not been met and that medical and food supplies were being blocked and failing to get to those who need them.

"We believe that the current conditions are not favourable for these negotiations, no aid has entered the besieged areas and detainees have not been released," he said.

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French President Francois Hollande, while echoing Merkel's comments, added that the "Syrian ceasefire must be respected everywhere and that the only actions which should be tolerated are those directed against ISIL and al Nusra".

"Any other initiative would violate the cessation of hostilities and be a pretext to not fully implement it," he said.

Hollande added that there was agreement to take advantage of the truce to coordinate humanitarian aid and open a process of political transition in Syria.

Following a Franco-British summit on Thursday, Hollande and UK Prime Minister David Cameron had expressed concerns that rebel forces continued to be targeted in Syria.

"We ask all sides that are committing human rights violations, including Russia and the Syrian regime, to put an immediate end to the attacks against moderate opposition groups," they said in a joint statement ahead of Friday's teleconference.

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Also on Thursday, Russia's defence ministry said in a statement it had registered 14 ceasefire violations in Syria over the past 24 hours.

The violations concerned the shelling of residential areas and Syrian government forces in the provinces of Damascus, Latakia, Hama and Deraa, it said.

Despite the sporadic attacks, the UN confirmed on Thursday that the conditional truce had made "visible progress", despite clashes in some cities and areas.

Staffan de Mistura, the UN envoy to Syria, said the level of violence in the county had been "greatly reduced".

"In general, the cessation has been holding," he added.