Warplanes have carried out air raids on parts of northern Syria as a top opposition official warned violations of a fragile ceasefire could jeopardise 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 ceasefire brokered by Russia and the US, the most ambitious effort yet to curb the violence of the country's five-year civil war. The truce has been holding since it went into effect at midnight on Friday despite accusations by both sides of violations.
The Britain-based Syrian Observatory for Human Rights said the air strikes 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 (LCC) said the warplanes were Russian.
The Observatory and the LCC also reported air raids on the north western town of Jisr al-Shughour saying a woman was killed and 12 others were wounded.
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.
Meanwhile Syria's state news agency said militants fired shells into government-held areas in the coastal province of Latakia from their bases near the Turkish border. The agency reported that the shelling killed and wounded a number of people, without giving further details.
Opposition activists and state media also reported clashes between troops and members of the Islamic State group mostly in the northern province of Aleppo. Still, both sides have said they will continue to abide by the truce.
Riad Hijab, who heads the High Negotiations Committee, an umbrella for opposition and rebel factions, said in a statement directed to UN chief Ban Ki-Moon that Russian, Iranian and government forces have not stopped hostilities since the truce went into effect.
Mr Hijab said there have been 24 cases of shelling and five cases of ground attacks. He added that Russian warplanes carried out 26 air strikes on Sunday alone targeting rebels that are abiding by the truce.
"The repeated violations by the regime and its allies have killed 29 and wounded dozens," he said, adding that the opposition is abiding by the ceasefire and warning that "resuming the negotiations process in such circumstances would be difficult".
UN Special Envoy to Syria Staffan de Mistura has called for a new round of indirect peace talks in Geneva on March 7, after the first round of talks collapsed earlier this month.
Meanwhile, the Russian military operating in Syria said it has information about an attack on the Syrian border town of Tal Abyad from Turkish territories with the use of large-calibre artillery and has asked the United States for an explanation.
Russia has set up a centre for monitoring the truce at the Hemeimeem air base in Syria, where Russian warplanes are based.