The Russian ceasefire monitoring center near Latakia says it is verifying reports of an attack on the Kurdish town Tell Abyad in northern Syria carried out by militants coming from Turkey.

The reports came overnight and claim that the forces coming from Turkey are using heavy artillery, according to Lt. Gen. Sergey Kuralenko, who heads the center for Syrian reconciliation.

“This information was verified though multiple channels, including representatives of the Syrian Democratic Forces (SDF), [a rebel alliance that includes Kurds, Arabs and other ethnic groups and operates in the region],” he said.

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Russia has requested clarification from the US-run counterpart of the center based in Amman, citing its influence on Turkey, a member of the US-led coalition fighting the Islamic State terrorist group, the general said.

The Turkish newspaper Hurriyet cited military sources as denying that the Turkish military were involved in any cross-border shelling on Sunday.

Leading world powers have brokered a shaky ceasefire in some parts of Syria, which is expected to be observed by all parties expect hardcore Islamist fighters of IS and Nusra Front.

READ MORE: Russia stops all Syria airstrikes on areas & armed groups included in ceasefire - General Staff

Turkey is currently leading a crackdown on Kurdish militias from the Kurdistan Workers' Party (PKK), which it considers a terrorist organization. While the crackdown is focus on predominantly Kurdish regions in south-eastern Turkey, the clashes occasionally spill across the border into regions of Syria and Iraq held by Kurds.

Kurdish militias in Iraq and Syria are one of the few forces on that successfully opposed the spread of Islamic State and have been supported by the US. Ankara criticized Washington's attitude, saying America should chose between the Kurds and the Turks.