BEIRUT — Warplanes carried out air raids Sunday on several parts of northern Syria as a top opposition official warned that continued violations of a partial cease-fire could jeopardize a planned resumption of UN-brokered peace talks.

The acts of violence came as Russia said a northern town held by a predominantly Kurdish militia came under fire from the Turkish side of the border.

Sunday’s air raids came on the second day of a cease-fire brokered by Russia and the United States, 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 in Aleppo province. The group did not say whether the warplanes were Russian or Syrian. The Local Coordination Committees said the warplanes were Russian.

The Observatory and the LCC also reported air raids on the northwestern town of Jisr al-Shughour.

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

Opposition activists and state media also reported clashes between troops and members of the Islamic State group mostly in the northern province of Aleppo.

Associated Press