"Seventeen fighters were killed in Turkish air strikes that hit several Syrian regime outposts... near the Turkish border," the Syrian Observatory for Human Rights said.

It did not specify if the victims were affiliated with the government or Kurdish forces.

At least three Syrian soldiers were among the dead and six were wounded in the Turkish raids, said the official SANA news agency, citing a military source.

"Any attack on a military outpost run by our armed forces will be met with a direct and immediate response on all fronts," SANA said.

The strikes took place near the Kurdish-held town of Kobane, the site of overnight clashes between Turkish forces and the Kurdish-led Syrian Democratic Forces (SDF).

Kurdish forces also struck inside Turkish territory overnight, killing one soldier, Turkey's defence ministry said.

"Thirteen terrorists were neutralised" in retaliatory attacks by Ankara inside Syria, the ministry said, adding that operations in the region were ongoing.

Turkey has stepped up its attacks in Kurdish-controlled areas of Syria since a July 19 summit with Iran and Russia failed to green-light a fresh offensive against Kurdish fighters viewed by Ankara as terrorists.

A Turkish drone strike on Tuesday killed at least four people in the Kurdish-controlled region of Hasakeh, the latest in a spate of similar attacks.

The SDF, the Syrian Kurds' de facto army, says it has counted at least 13 of its members killed in Turkish attacks since July.

Turkey has launched a series of cross-border offensives targeting Kurdish forces and the Islamic State group since 2016, but such operations have rarely resulted in the killing of Syrian regime fighters.

Regime forces have deployed in areas controlled by Kurdish fighters near the border with Turkey as part of agreements intended to stem a fresh Turkish operation.

Turkey has fervently opposed Syrian President Bashar al-Assad, backing rebels calling for his removal and opening its doors to refugees.

But last week, Turkish Foreign Minister Mevlut Cavusoglu called for reconciliation between the Syrian government and the opposition.

His comments were seen as an apparent easing of Ankara's long-standing hostility towards Assad's government and enraged the Syrian opposition and rebel groups.