At least 24 civilians were killed Wednesday in air raids on a rebel-held area of Aleppo and an Islamic State-held village nearby, a Syrian monitoring group said.

Fourteen people were killed in the airstrikes on Tadef, near the town of al-Bab, the Syrian Observatory for Human Rights said.

Local opposition sources said the raids were carried out by Turkish forces. That information could not be independently verified.

Al-Bab lies about 30 kilometres south of the border town of al-Rai, one of the centres of Turkey's recent ground intervention in support of Syrian rebels against Islamic State and Kurdish-led forces.

It also lies about 25 kilometres from positions held by the Kurdish-led forces who last month captured the city of Minbij from Islamic State. Government forces are also positioned close to al-Bab.

Both rebels and the Kurdish-backed forces have said they intend to move on al-Bab. Capturing the town would allow the Kurds to link up their main territory in north-eastern Syria with an enclave they control in the north-west.

Turkey and the rebels are adamantly opposed to the formation of a Kurdish entity spanning northern Syria.

In Aleppo's eastern al-Sukari district, meanwhile, the Observatory reported that 10 people were killed in air raids, a day after activists there reported a poisonous gas attack in which 22 people died and 40 others were wounded.

Ibrahim al-Hajj, a spokesman for the volunteer Syrian emergency group White Helmets, said that four rescue workers from his organization, which works in opposition-held areas of the country, were killed in air raids over the past 24 hours in and near Aleppo.

The international chemical weapons watchdog said it was "disturbed" by reports of chlorine gas use in an air raid Tuesday in al-Sukari.

The Observatory said later Wednesday that six members of the Asayesh Syrian Kurdish security force were killed in cross-border shelling by Turkish forces. They were killed near the Turkish border in the Kurdish enclave of Efrin in north-western Syria.

Wednesday's developments came as Russia announced that its Foreign Minister Sergei Lavrov would meet US Secretary of State John Kerry in Geneva on Thursday and Friday to discuss Syria.

The two top diplomats spoke by phone on Wednesday to build on a discussion about Syria between their countries' heads of state on the sidelines of the G20 summit in China earlier this week, the Russian Foreign Ministry said.

The US State Department confirmed the phone call, and said Kerry remains committed to continuing efforts to reach a ceasefire. But spokesman Mark Toner didn't confirm that Lavrov and Kerry would meet, saying at this time he has no travel to announce.

"What I'm saying right now is that we don't have anything to confirm," Toner said.

In Geneva, Kerry and Lavrov are also expected to discuss measures to broaden the distribution of humanitarian aid to Syrian civilians, the Russian statement said.

Russia intervened in Syria a year ago to prop up the regime of President Bashar al-Assad, a long-standing ally whose overstretched army was rapidly losing ground to rebel forces.

Moscow's intervention allowed the government to win back some ground, notably imposing a siege on eastern Aleppo where some 250,000 to 300,000 residents are now thought to be trapped.

Rights groups have also blamed the Russian air campaign for deadly airstrikes that have hit civilian targets including hospitals.

The US has given cautious support to the Syrian opposition but its main priority in Syria is combatting the Islamic State extremist organization as well as Jabhat Fatah al-Sham, an al-Qaeda-linked force which is one of the strongest rebel groups.

The Syrian conflict, which started with peaceful protests against al-Assad's regime in 2011, has developed into a four-way conflict between government forces, mainly Islamist rebels, Islamic State, and leftist Kurdish-led forces.

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