GAZIANTEP, Turkey — Syria’s hard-won truce began to fray Sunday, with Russian warplanes resuming airstrikes on towns and villages in the north and fresh reports of artillery fire across several front lines.
The violence came on only the second day of a planned two-week cessation of hostilities, dimming hopes that the calm that took hold Saturday will endure long enough to inject new impetus into a wider peace effort.
The Russian planes, based in northwestern Syria, struck six towns and villages in the provinces of Aleppo, Hama and Idlib early Sunday, according to monitoring and civil defense groups.
The strikes ended a 24-hour suspension announced by the Russian military on Saturday to coincide with the launch of the truce. They also appeared to signal a return to attacks that preceded the effort to end the fighting, in which Russia has helped bolster the fortunes of President Bashar al-Assad, a longtime ally.
Russia’s Defense Ministry offered no comment on the strikes, but it had warned Saturday that it reserved the right under the terms of the truce to continue hitting the Islamic State and Jabhat al-Nusra, terrorist groups that are battling the Assad regime.
Russian warplanes have in the past repeatedly struck towns loyal to more-moderate rebels, including those backed by the United States, while claiming that they were targeting the Islamic State or Jabhat al-Nusra, which is affiliated with al-Qaeda.
The first half-dozen attacks on Sunday, carried out shortly after 6 a.m., awoke residents in four towns west of Aleppo that lie on the last rebel supply route into the city, according to the White Helmets civil defense group. Videos posted on YouTube showed damage to shops and houses.
Shortly after, bombs struck the town of Harb Nufsa in Hama. On Sunday afternoon, two strikes hit civilian areas of the northern town of Jisr al-Shughour, which is controlled by a coalition of fighters that includes Jabhat al-Nusra. A pregnant woman was killed and 12 people were injured, the White Helmets said.
The total number of strikes was nonetheless significantly lower than in the days preceding the truce, when Russia dropped hundreds of bombs over a wide area of rebel-held territory in an apparent attempt to score last-minute gains. Although artillery and small-arms fire by both sides were reported on a number of front lines, the intensity of the fighting appeared to have eased significantly.
On Sunday morning, Russia’s Defense Ministry said the truce appeared to be working.
“On the whole, the ceasefire regime in Syria is being implemented,” the ministry said in a statement, according to Russian news agencies.
A cease-fire coordination center set up at the Russian air base of Khmeimim, in northwestern Syria’s Latakia province, accused the rebels of committing nine truce violations in the first 24 hours, singling out an attack by the Islamic State on the Kurdish-held town of Tal Abyad in the northeast as the most serious.
The head of the coordination center, Lt. Gen. Sergei Kurylenko, claimed in televised remarks that Turkey facilitated that attack and that the incursion was “supported by artillery fire from Turkish territory.” He said Russia had lodged a complaint with the U.S. cease-fire coordination center, based in the Jordanian capital, Amman.
Turkey denied the charge, according to military sources quoted by the website of the Turkish newspaper Hurriyet.
The Islamic State’s incursion into Tal Abyad was the most serious by the militant group in northeastern Syria in more than eight months and was contained only after U.S. warplanes intervened. On Sunday, reports from Tal Abyad said militants were still holed up on the outskirts.
Zakaria Zakaria contributed to this report.