At least 13 people have been killed in a car bomb explosion in the Syrian town of Tal Abyad on the border with Turkey, according to the Turkish defence ministry.

"Based on first findings, 13 civilians were killed and around 20 others injured" in the explosion in the northeastern town, Turkey's defence ministry said in a statement on Saturday.

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The town has witnessed some of the heaviest fightings since the Turkish military launched an operation last month in northeast Syria against the Kurdish armed group People's Protection Units (YPG), which for years was allied to the United States in the fight against the Islamic State of Iraq and the Levant (ISIL or ISIS) group.

The Syrian Observatory for Human Rights said pro-Turkey fighters and civilians were among the dead and injured in the car explosion.

"We condemn this inhuman attack of the bloody PKK/YPG terrorists who attacked the innocent civilians of Tal Abyad who returned to their homes and lands as a result of the Operation Peace Spring," Turkey's defence ministry said on Twitter.

No group has yet taken responsibility for the attack.

Battle for northeast Syria

The Turkey-based Kurdistan Workers Party (PKK) is designated a terrorist group by Ankara and its Western allies. The PKK launched a separatist rebellion against the Turkish state in 1984.

Ankara considers the YPG a terrorist group because of its ties to PKK Kurdish rebels in southeast Turkey.

On October 9, days after President Donald Trump's abrupt decision to pull out US troops, Turkey and allied Syrian rebels launched a cross-border operation and seized control of Tal Abyad and some 120km (75 miles) of land along the frontier.

A "safe zone" area between Tal Abyad and the Syrian town of Ras al-Ain was established as part of an October 17 deal between Ankara and Washington, involving a ceasefire and the YPG's full withdrawal from the stretch.

On Friday, Turkish and Russian troops in armoured vehicles held their first joint ground patrols in northeast Syria under a deal between the two countries that forced the YPG away from territory near Turkey's border.