Syrian activists said airstrikes targeting the Islamic State group's de facto capital of Raqqa on Thursday killed at least 20 civilians, as neighboring Turkey called for greater cooperation with Russia against the extremist group.

The offer by Turkish Foreign Minister Mevlut Cavusoglu followed a meeting between the Russian and Turkish leaders in which they agreed to mend ties.

Cavusoglu also announced that his country will resume its airstrikes against IS targets in Syria, months after they were suspended amid a major row with Moscow. He said in an interview with Turkey's private NTV television that Ankara "will again, in an active manner, with its planes take part in operations" against IS targets.

Turkey had temporarily suspended its limited participation in the airstrikes campaign by the U.S.-led coalition, following soured relations with Moscow after Turkish air force jets downed a Russian warplane on the Syrian border in November. Russia had retaliated by deploying long-range air defense missile systems to its base in Syria, 30 miles south of the border with Turkey and imposing an array of economic sanctions.

"On the issue of Daesh, we have made a call to Russia. We said we have a common enemy which we can struggle against together," Cavusoglu said, using an Arabic language acronym for IS.

The local activist group Raqqa is Being Slaughtered Silently meanwhile said the airstrikes on Raqqa killed at least 20 civilians and cut the city's water supply. The Britain-based Syrian Observatory for Human Rights said 24 civilians were killed, along with six others whose affiliation or identities could not yet be confirmed.

Both groups said the strikes were launched by Russian jets, though it was not clear how they made that determination. The Russian military said six of its long-range bombers had flown from their base in Russia to strike IS facilities near Raqqa, but did not mention civilian casualties. It said the raid destroyed a large ammunition depot, a plant producing chemical weapons and a large IS training camp.

Meanwhile, there was no letup in the embattled northern Syrian city of Aleppo, where Turkey and Russia are supporting opposing sides of the conflict and where residents and activists reported a chlorine gas attack.

A Syrian rescue worker and opposition activists said Thursday that a Syrian government airstrike on an opposition-held district killed at least two people in what was alleged to have been a chlorine gas attack. At least four barrel bombs were dropped late Wednesday on the city's eastern Zabadieh neighborhood, one of which purportedly released the chlorine gas.

Wissam Zarqa, a local resident, described gasping for breath and cowering with his family on the top floors of their apartment building as a gas filled the hallway.

A Syrian military official denied the allegations, saying militants had fabricated the news. The official, based in Damascus, Syria, spoke on the condition of anonymity because he is not authorized to give official statements.

The accusations came hours after the Russian military, which is fighting alongside Syrian government forces, promised a daily, three-hour cease-fire for Aleppo to allow humanitarian aid into besieged areas. Lt. Gen. Sergei Rudskoi, of the Russian military's General Staff, said the cease-fires will be observed from 10 a.m. to 1 p.m. local time starting Thursday.

However, there was no letup to the fighting in Aleppo, and residents of the opposition-held east reported near-constant fighter jet overflights on Thursday. "I'm at home and I don't dare to leave -- the jets are not letting up," Zarqa told the AP.

A senior U.N. humanitarian official, Jan Egeland, said the Russian offer of a daily truce "is really nothing. We need 48 hours." Speaking in Geneva, he said that Russia has agreed to hold talks with U.N. officials to hammer out a "workable" plan for a humanitarian pause in Aleppo.

The Organization for the Prohibition of Chemical Weapons (OPCW) said Thursday that reports of possible chemical weapons use in Syria "are of great concern" and said it continues to examine any credible reports it received.

Khaled Harah, a first responder in the rebel-held part of Aleppo, said a government helicopter dropped four barrel bombs on Zabadieh and that one of them released chlorine gas, leading to the deaths of a mother and her two children.

The report, which was posted online Thursday, could not be independently verified.

The Observatory, which tracks the civil war in Syria, also reported that government barrel bombs struck the neighborhood. It had reports of two killed and several people suffering breathing difficulties -- but made no mention of chlorine gas.

Abdelkafi al-Hamdu, a resident of Aleppo, said he saw two air strikes from his in-laws' balcony, about 30 yards away. He said the first blast released a gas he identified by the smell as chlorine, but the wind was blowing in the other direction, lessening the odor.

He took cover in the apartment but began experiencing severe difficulties breathing, so he took his wife and daughter and tried to leave the building. But the odor grew stronger as they descended the stairs, so they returned to the higher floors to wait out the effects. He spoke to the AP via a messaging service.

The Syrian government and rebels have accused each other of using chlorine gas and other chemical weapons on several occasions throughout the five-year-old civil war. Last week, the Syrian government and the opposition traded accusations of using chlorine in Aleppo.

Chlorine has a number of civilian applications but can also be used as a crude weapon. It is fatal in high concentrations, while in lower doses it can damage lungs or cause severe breathing difficulties, vomiting and nausea.