Turkey has said its military is not targeting Syrian Kurds, after Kurdish forces and a monitoring group said tanks shelled Kurdish-held villages in northern Syria.
Ankara on Monday said it was investigating the reports of shelling. If confirmed, it would be the most serious incident yet of Turkey targeting Kurdish-controlled areas in the Syrian conflict.
Kurdish officials told Al Jazeera on Monday that overnight shelling targeted a checkpoint in a village outside Kobane manned by the Burkan al-Furat (Euphrates Volcano) battalion, a coalition of fighters from the Free Syrian Army and the Kurdish People's Protection Units (YPG).
The Syrian Observatory for Human Rights said four fighters were injured in the shelling.
"A number of shells fired by Turkish tanks fell on the village of Zur Maghar, which is controlled by the Kurdish People's Protection Units [YPG]," the UK-based monitoring group said.
Zur Maghar lies along the border with Turkey, in Aleppo province.
The YPG has proved to be Syria's most effective force against the Islamic State of Iraq and the Levant (ISIL), but its successes have been eyed suspiciously by Turkey because of its links to the Kurdistan Workers' Party (PKK), which Ankara considers to be a terrorist organisation.
Earlier this month, Syria's main Kurdish party, the Democratic Union Party (PYD), warned Turkey that any military intervention would threaten international peace and said its armed wing, the YPG, would face any "aggression".
Last week, Turkey launched two military campaigns, one hitting ISIL in Syria, and the other targeting the PKK in Iraq, which has strong links to the YPG in Syria.
The campaigns came after a suicide bombing in the Turkish town of Suruc killed 32 people.
On Monday, a Turkish official told the AFP news agency that "the ongoing military operation seeks to neutralise imminent threats to Turkey's national security and continues to target ISIL in Syria and the PKK in Iraq", adding that "PYD, along with others, remains outside the scope of the current military effort".
A YPG official told Al Jazeera that in a previous incident, Turkey had fired at a car belonging to the Kurdish militia in Kobane on Wednesday.
"We thought it was a mistake. But last night the shelling lasted for half an hour. So obviously it's not a mistake," the official said.
Syrian Kurdish activist Mustafa Ebdi also reported overnight shelling.
"Now the YPG is facing attacks from IS [ISIL] and Turkey," he told the AP news agency.
Source: Al Jazeera and agencies