BEIRUT - The toll in Turkish air raids on Kurdish positions in northeastern Syria rose to 28 killed, a monitor said Wednesday, a day after Ankara said it had targeted "terrorist havens" near its border.

The Syrian Observatory for Human Rights said most of those killed were members of the Kurdish People's Protection Units (YPG), which is battling the Islamic State group in northern Syria.

Observatory director Rami Abdel Rahman said 19 others were wounded in the Tuesday raids on a media centre and other buildings in Al-Malikiyah, a town in Hasakeh province.

YPG spokesman Redur Khalil on Tuesday said 20 fighters were killed and 18 wounded in the Turkish strikes, which the United States said were carried out without the knowledge of a Washington-led international coalition fighting IS in Syria and neighbouring Iraq.

Abdel Rahman said a female Kurdish fighter was among the dead.

READ: Spate of attacks in Turkey blamed on PKK

Turkey, which backs Syrian rebel groups and which launched a ground operation in northern Syria last year, vowed to continue acting against groups it links to the outlawed Kurdistan Workers' Party (PKK).

It also killed six Kurdish peshmerga fighters in northern Iraq on Tuesday in an apparent accident.

The strikes underlined the complexities of the battlefields in Iraq and Syria, where twin US-backed offensives are seeking to dislodge IS from its last major urban strongholds.

They could also exacerbate tensions between Ankara and its NATO ally Washington, which sees the Kurds as instrumental in the fight against IS.