Syria's fragile ceasefire entered a second day on Sunday with battlezones still largely quiet for the first time in five years, despite sporadic incidents including several air strikes.

The truce, brokered by Washington and Moscow, is seen as a crucial step towards ending a conflict that has claimed 270,000 lives and displaced more than half the population.

The convoluted patchwork of territorial control in Syria, wrapped up in a brutal civil war since 2011, has complicated efforts to implement the deal.

Warplanes, believed to be either Syrian or Russian, bombed seven villages Sunday in the northern province of Aleppo and Hama in the centre, according to the Syrian Observatory for Human Rights.

It was unclear if the raids hit areas covered by the ceasefire, which excludes territory held by the Islamic State jihadist group and Al-Qaeda affiliate Al-Nusra Front.

According to Observatory head Rami Abdel Rahman, only one of the villages, Kafr Hamra in Aleppo province, is controlled by Al-Nusra and the others are in the hands of non-jihadist rebels.

Elsewhere the situation remained mostly calm, according to AFP reporters.

In Aleppo, Syria's second city, residents took to the streets to do their shopping after a night without any sound of fighting or air strikes, a correspondent said.

"There's something strange in this silence. We used to go to sleep and wake up with the sound of raids and artillery," said Abu Omar, 45, who runs a bakery in rebel-held east Aleppo.

- Damascus shelling -

A task force set up to monitor the deal described it on Saturday as largely successful on the first day.

"The United Nations, the United States and Russia have made a positive assessment of the first hours of the cessation of hostilities," a Western diplomat said after a meeting of the International Syria Support Group in Geneva.

The UN reported "some incidents" in apparent violation of the truce, but "they have been defused", he said.

Russian Foreign Minister Sergei Lavrov's office said he and US Secretary of State John Kerry had "hailed" the ceasefire in a phone call, and discussed ways of improving cooperation between their militaries.

UN envoy Staffan de Mistura has said peace talks will resume on March 7 if the ceasefire prevails and more aid is delivered -- a key sticking point in negotiations.

A spokesman for the UN's humanitarian affairs office said the next aid convoys were expected to leave on Sunday if conditions on the ground are right and the necessary approvals are received.

"If it (the truce) holds, it will create the conditions for full, sustained and unimpeded humanitarian access throughout Syria," said EU foreign policy chief Federica Mogherini.

Russia, which has waged nearly five months of intense air strikes in support of Syrian President Bashar al-Assad, said Saturday that it had halted bombing in all areas covered by the truce.

Moscow has vowed to keep striking IS, Al-Nusra and other "terrorist groups."

The ceasefire breaches on Saturday included shells hitting Damascus, according to Syrian state media, and others hitting a majority-Kurdish neighbourhood in Aleppo city, the Observatory said.

The city is now almost completely encircled by pro-regime troops after a massive Russian-backed offensive that has caused tens of thousands to flee.

Since the truce began, however, locals have taken to the streets to enjoy the calm as children play in parks.

- Suicide bombings -

Kurdish forces and their Arab allies pushed back an IS attack on the border town of Tal Abyad in Raqa province on Saturday, the Observatory said.

The clashes and strikes by a US-led coalition killed 70 jihadists. Another 20 Kurdish militiamen and two civilians were also killed.

Twin suicide bombings meanwhile killed six people outside a town in Hama province, where IS is present, state news agency SANA said.

The complexities of a conflict which escalated from anti-government protests into a full-blown war drawing in rival world powers make brokering a lasting ceasefire a major challenge.

Assad has been bolstered by support from Russia and Iran while the West, Turkey and Gulf states back rebel groups.

Syria's top opposition grouping, the High Negotiations Committee, said Friday that 97 opposition factions had agreed to respect the truce, for two weeks initially.

Neighbouring Israel, an arch-foe of Tehran, welcomed the ceasefire but warned it would not accept Iranian "aggression" or the supply of advanced weapons to Hezbollah, the Lebanese Shiite militia supporting Assad.

"It's important it remains clear any agreement in Syria must include an end to Iranian aggression aimed at Israel from Syria's territory," Prime Minister Benjamin Netanyahu said.

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