Turkey has launched air strikes over several towns in northern Syria, US-backed Kurdish-led forces report.
The strikes occurred a week after a bomb rocked a bustling avenue in the heart of Istanbul, killing six people and wounding over 80 others.
Turkish authorities blamed the attack on the outlawed Kurdistan Workers' Party, or PKK, as well as Syrian Kurdish groups affiliated with it. The Kurdish militants groups have, however, denied involvement.
Ankara and Washington both consider the PKK a terror group, but disagree on the status of the Syrian Kurdish groups, which have been allied with the US in the fight against the Islamic State group in Syria.
The air strikes targeted Kobani, a strategic town near the Turkish border that Ankara had previously attempted to overtake in its plans to establish a "safe zone" along northern Syria.
Syrian Democratic Forces (SDF) spokesperson Farhad Shami in a tweet added that two villages heavily populated with displaced people were under Turkish bombardment.
Syrian opposition media reported that Turkish air strikes targeted Kurdish-led SDF positions.
No casualties were reported.
In neighbouring Iraq, the US Consulate General in Erbil said it is monitoring "credible open-source reports" of potential Turkish military action in northern Syria and northern Iraq in the coming days.
The Kurdish-led authority in northeast Syria said on Saturday that if Turkey attacks, then fighters in the area would have "the right to resist and defend our areas in a major way that will take the region into a long war."
Turkey has launched three major cross-border operations into Syria since 2016 and already controls some territories in the north.