Saudi Arabia on Sunday accused President Bashar al-Assad's regime and its ally Russia of ‘ceasefire violations’ in Syria.

‘There are violations to the ceasefire from Russian and (Syrian) regime aircraft,’ Saudi Foreign Minister Adel Jubeir told reporters in Riyadh.

‘We are discussing this with (the 17-nation) Syria Support Group,’ co-chaired by Russia and the United States, said Jubeir.

The Syrian Observatory for Human Rights has said that several air strikes hit central and northern Syria on Sunday.

Warplanes, believed to be either Syrian or Russian, bombed seven villages in the provinces of Aleppo and Hama, the monitor said.

A ceasefire brokered by Moscow and Washington took effect at midnight Friday but the Riyadh-based opposition and Russia have reported several breaches from opposing sides.

The ceasefire agreement does not include territory held by the Islamic State jihadist group and Al-Qaeda-affiliated Al-Nusra Front, which together control more than half of Syria.

Russia, which has waged five months of intense air strikes in support of Assad, said Saturday it had halted bombing in all areas covered by the truce.

But it has vowed to keep striking IS and Al-Nusra and other ‘terrorist groups’.

It was unclear if Sunday's raids hit areas covered by the truce.

But Jubeir said that Russia was targeting Syria's ‘moderate opposition’ groups.

UN special envoy Staffan de Mistura was ‘in contact with the Russians and the Syrian regime on this matter to reach an agreement that would limit or end military operations against the moderate Syrian opposition and focus instead on Daesh (Arabic acronym for IS) and Al-Nusra,’ said Jubeir.

‘Things will become clearer in the coming days on whether the regime and Russia are serious or not about the ceasefire,’ he added.

Saudi Arabia is a main supporter of the Syrian rebels battling Assad's regime since 2011.