As pivotal fighting unfolds in Syria and Iraq, NATO ally Turkey is showing itself to be more and more of a wild card, fueling complications on a pair of already chaotic battlefields.
Turkey's military said Thursday that it had killed up to 200 Kurdish-led fighters in a series of overnight strikes north of the divided Syrian city of Aleppo. That claim was questioned by Kurdish commanders, who reportedly put the number of deaths in the low double digits, but said the strikes were continuing.
Whatever the toll turns out to be, it was the latest instance of Turkey lashing out at American-backed forces in a volatile contested area — suggesting the government of President Recep Tayyip Erdogan will act aggressively to safeguard its own interests, even at the expense of the anti-Islamic State coalition in which it is a partner.
Erdogan's government fears that Kurdish territorial gains inside Syria will embolden their autonomy-minded ethnic kin in southeastern Turkey — particularly the fighters of the Kurdistan Workers Party, or PKK, which Turkey has branded a terrorist organization.
"It's a recipe for prolonged instability," said Aaron Stein, a resident fellow at the Atlantic Council, a Washington-based think tank, referring to the escalating clashes between forces arrayed against Islamic State in northern Syria.
That pattern is on plain display as well in Iraq, where U.S.-supported Iraqi forces and Kurdish peshmerga fighters have launched a long-awaited offensive to dislodge the Sunni militant group from Mosul, the largest city under the group's control.
Turkey insists it will play a part in the Mosul operation, worsening the power struggles that are likely if and when the city is retaken. The alliance is marked by festering feuds along ethnic and sectarian lines, which are playing out even amid the fighting and likely to flare fiercely afterward.
Erdogan's government, citing a previous deal with Baghdad, has deployed about 500 troops at a base north of Mosul, in defiance of the wishes of Iraqi Prime Minister Haider Abadi. That set off an angry verbal volley between the Turkish and Iraqi leaders in recent days, with Erdogan admonishing Abadi to "know your place."
Abadi responded with a derisive reference to the attempted coup against Erdogan in July, which the Turkish leader beat back in part with deft use of social media to rally his loyalists.
In a sign of deepening tensions, an Iraqi court has issued an arrest warrant against the former governor of Nineveh, the Iraqi province of which Mosul is the capital, accusing him of paving the way for the Turkish military deployment in northern Iraq, news agencies reported Thursday.
In Syria, the anti-Islamic State alliance is fraught with a central point of tension: Although it supports rebels seeking to topple Syrian President Bashar Assad, the Ankara government considers Kurdish forces to be a greater threat than Islamic State, and has acted accordingly.
The airstrikes late Wednesday and early Thursday, detailed in a military statement carried by Turkey's state-run Anadolu news agency, were the most significant single attack by Turkish forces on Kurdish-led fighters since the start two months ago of a Turkish military incursion into northern Syria.
That action was ostensibly in support of Syrian rebels fighting Islamic State, but was also a clear warning to some Kurdish factions to not attempt to enlarge their existing beachhead along Syria's border with Turkey.
Erdogan unleashed more bellicose rhetoric Wednesday, declaring in a speech that Turkey would not hesitate to act on its own to "root out" its enemies.
"We will not wait until the blade is against our skin," he said. "We will not wait for terrorist organizations to come and attack us."
Since the crumbling of a cease-fire last year, Turkish forces have been raking the PKK's southeastern mountain strongholds with airstrikes and artillery fire, killing hundreds of civilians in the process.
In northern Syria, the People's Protection Units, or YPG, the U.S.-allied Kurdish militia, said in a statement Thursday that Turkish warplanes had aimed almost 20 overnight airstrikes at fighters from an affiliated group, Jaish al-Thuwar, which was pushing forward against Islamic State-held areas.
Kurdish fighters have been moving east in the direction of Al Bab, which they and other Syrian rebels hope to capture from Islamic State. Turkey's military confirmed 26 strikes on areas that had recently come under YPG control, estimating that between 160 and 200 combatants had been killed.
At the Pentagon, Defense Secretary Ashton Carter, who was due to visit Turkey on Friday, was asked whether the airstrikes raised concern about the alliance with Ankara.
"With respect to Turkey, our partnership is very strong" in the campaign against Islamic State, he said. "We're working with the Turks now very successfully to help them secure their border area."
Stein, the analyst, called the clashes around Al Bab a microcosm of a much larger problem in Syria — the hodgepodge of anti-Islamic State forces that are at one another's throats. "In the strangest of ways," he said, Islamic State, also known as ISIS, serves as a kind of buffer between them.
"When you remove ISIS," he said, "you simply create conditions for more conflict among the anti-ISIS opposition."
Times staff writer King reported from Washington and special correspondent Umar Farooq from Athens.