Turkish warplanes killed more than 20 Kurdish fighters Tuesday in strikes in Syria and Iraq, where the Kurds are key players in the battle against the Islamic State group.
Turkey said it had carried out the strikes in northeastern Syria and northern Iraq against "terrorist havens" and vowed to continue action against groups it links to the outlawed Kurdistan's Workers' Party (PKK).
In northeastern Syria strikes targeting the Kurdish People's Protection Units (YPG) -- who are leading the offensive against IS stronghold Raqa -- killed at least 18 people.
In northern Iraq they killed six Peshmerga fighters from the autonomous Kurdish government, usually allied with Ankara, in an apparent accident. The Peshmerga said the strike was "unacceptable" but blamed PKK-affiliated militia who were the apparent targets.
The strikes underlined the complexities of the battlefields in Iraq and Syria, where twin US-backed offensives are seeking to dislodge IS jihadists from their last major urban strongholds.
They could also exacerbate tensions between Ankara and its NATO ally Washington, which sees the Kurds as one of the most effective fighting forces against IS.
Turkey's army said it launched the strikes "in order to destroy terrorist havens targeting our country".
"The operations will continue to be carried out from now with the same determination until the very last terrorist is neutralised," the army said.
The bombardment in northeastern Syria saw Turkish planes carry out "dozens of simultaneous air strikes" on YPG positions overnight, including a media centre, a monitoring group said.
The strikes killed three media officers and 15 YPG fighters, one of the highest death tolls from Turkish air raids on Kurdish militia, according to Rami Abdel Rahman, the head of the Syrian Observatory for Human Rights.
In a statement distributed to journalists, the YPG confirmed the Turkish bombardment and said there were casualties but did not give a toll.
Representatives of the US-led coalition visited the site of the air strikes on Tuesday, the YPG's political arm, the Democratic Union Party (PYD), said on Twitter.
The PYD published photographs of YPG officials walking alongside a man in a military uniform with a patch bearing a US flag on his chest.
A YPG commander urged the coalition to act to prevent further Turkish attacks.
"It's unthinkable that we are fighting on a front as important as Raqa while Turkish planes bomb us in the back," the commander said.
Ankara has bombed the YPG across swathes of northern Syria for months, calling it a "terrorist" group because of its ties to the PKK, which has been waging a deadly insurgency against the Turkish state since 1984.
While the air raids on Syria appeared to hit their intended targets, the bombardment in Iraq instead killed members of Kurdish security forces that are typically allied with Ankara.
The Peshmerga ministry in Iraq's autonomous Kurdish government said the Turkish raids killed five of its fighters and one intelligence officer.
Turkey appeared to have been targeting a minority Yazidi militia allied with the PKK and based in the northwestern region of Sinjar.
The Peshmerga denounced the strike as "unacceptable" but focused blame on PKK-affiliated groups.
"These problems and tensions are all because of the PKK's presence," it said.
The Peshmerga have been instrumental in the battle against IS in northern Iraq though have stepped back in recent weeks as Iraqi forces advance against IS in Mosul.
Iraqi forces on Tuesday announced they had retaken full control of the Tenek district, one of the largest neighbourhoods in west Mosul.
The eastern side of the city was recaptured in January and a push on the western half launched the following month has made steady progress despite fierce resistance.
IS is facing multiple offensives across Syria and Iraq -- often led by governments or forces that are otherwise bitterly opposed to each other.
Turkey launched an unprecedented cross-border operation into Syria in August to fight IS and to keep the YPG in check.
The YPG makes up the bulk of the Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters taking on IS jihadists in Syria.
After chipping away at IS territory across the country's north, the SDF is now locked in clashes against the jihadists inside Tabqa, a key town on the Euphrates River.
Fighting continued inside the town's south and west on Tuesday, backed by heavy US-led air strikes overnight, according to the Observatory.
The SDF entered the town on Monday as part of their flagship offensive for Raqa, the Syrian heart of the jihadists' self-styled "caliphate" since 2014.
More than 320,000 people have been killed in Syria's six-year conflict, which the World Health Organization has called the most dangerous place for health workers.
Air strikes on a rebel-held village in northwestern Syria early Tuesday killed 12 people and put a nearby field clinic out of service, according to the Observatory.
The dead, which included at least two rebels and five civilians, were killed in a first round of raids on the village of Duwayleh in Idlib province.
As medics were bringing wounded people for treatment at a field clinic nearby Kafr Takharim, air strikes hit the facility and put it out of service.