Syria’s main opposition grouping recorded 15 violations by government troops and allied forces on the first day of a landmark truce, a spokesman told reporters Sunday, as Russia accused Turkey of breaking the ceasefire.

“There were 15 violations by the regime forces on day one of the ceasefire, including two attacks by (Lebanese militant group) Hezbollah in Zabadani” west of Damascus, said Salem al-Meslet, spokesman for the High Negotiations Committee.

Opposition monitoring groups reported earlier Sunday that warplanes had carried out air raids on two villages in northern Syria.

Sunday’s air raids came on the second day of a cease-fire brokered by Russia and the US, the most ambitious effort yet to curb the violence of the country’s five-year civil war.

The Britain-based Syrian Observatory for Human Rights said the airstrikes hit the villages of Daret Azzeh and Qobtan al-Jabal. The group did not say whether the warplanes were Russian or Syrian.

The Local Coordination Committees said the warplanes were Russian.

It was not immediately clear if the warplanes struck areas controlled by al-Qaida’s branch in Syria, known as the Nusra Front. Both the Nusra Front and the Islamic State group are excluded from the truce.

The Russian military meanwhile reported that armed groups had attacked a Syrian town from Turkish territory, adding it had demanded an explanation from the United States.

“Overnight from February 27 to 28 the Russian center for the reconciliation of the warring parties in Syria received information about an attack from Turkish territory on the Syrian town of Tal Abyad by armed units using large-scale artillery,” said the chief of the center, Lieutenant General Sergei Kuralenko.

“This was subsequently verified and confirmed through several channels including representatives of the Syrian Democratic Forces,” Kuralenko was quoted as saying by Russian news agencies from the Hmeimim airbase.

The Syrian Democratic Forces is a US-backed Kurdish-Arab alliance.

“The Russian center has turned for an explanation to the Amman-based US center for reconciliation,” Kuralenko added, stressing that Turkey was a member of a US-led coalition.

No other details were provided by the Russian side.

According to the Syrian Observatory for Human Rights, the Kurdish forces and their Arab allies successfully pushed back a fierce IS offensive by Saturday night with backing from the US-led coalition.

In a statement published late Saturday, the Kurdish People’s Protection Units (YPG) accused a group of “IS mercenaries” of launching an attack on Tal Abyad from Raqa to the south and from Turkish territory to the north late Friday.

They said they were able to repel the attack but that clashes were ongoing.

A ceasefire brokered by Moscow and Washington took effect from 2200 GMT Friday and was largely holding on Sunday.

There was no immediate confirmation of the Russian report from Turkey.

Turkey said earlier the ceasefire deal was not binding for Ankara if its national security was threatened.