A woman after having her nails painted with the colors of the flag of the Kurdistan Workers Party (PKK), during a gathering celebrating Newroz, which marks the arrival of spring and the new year, in the border town of Suruc, Sanliurfa province, on March 17. REUTERS/Umit Bektas A senior US official has accused Turkey of pulling a bait-and-switch by using a recent anti-Islamic State agreement with the US as a "hook" to attack the Kurdish PKK in northern Iraq, The Wall Street Journal reports.

"It's clear that ISIL was a hook," the senior military official told The Journal, referring to the Islamic State (aka ISIS, ISIL, or Daesh).

"Turkey wanted to move against the PKK, but it needed a hook."

On Tuesday, an American military source told Fox News that US military leaders were "outraged" when Turkey began its bombing campaign, giving US special forces stationed in northern Iraq virtually no warning before Turkish jets started striking the mountains.

"A Turkish officer entered the allied headquarters in the air war against ISIS and announced that the strike would begin in 10 minutes and he needed all allied jets flying above Iraq to move south of Mosul immediately," the source said. "We were outraged."

The confrontation highlights the tension growing between the US and Turkey, which became a reluctant ally in the fight against ISIS after years of turning a blind eye to the militants' illicit activity on its southern border during the Syrian civil war.

Ankara officially joined the coalition fight against ISIS on July 24, striking ISIS (and the PKK) on the same day. It also recently began allowing the US to use the Incirlik airbase in Turkey to carry out strikes against ISIS.

But Turkey has conducted 300 strikes against the PKK and three against ISIS since July 24, according to data compiled by IRIN news. All three ISIS strikes occurred on the first day of the campaign.

Nearly 400 Kurdish militants have been killed, IRIN reports, compared with nine ISIS militants.

When asked about Turkey's commitment to fighting ISIS, a senior defense official said "there are still question marks out there. Our folks are very eager to put it to the test.”

And if Turkey keeps going after the PKK while trying not to provoke ISIS, "it will leave the US without a Syria strategy," geopolitical expert Ian Bremmer told Business Insider by email.

"Access to Incirlik airbase matters, but the additional bombing it enables will only help contain ISIS, not roll it back," Bremmer added. "And it will leave Washington without the improved relations with Ankara that the Obama administration is hoping for."

The ongoing bombing campaign against PKK strongholds in northern Iraq came as a surprise, but it probably shouldn't have: Turkey has long seen the PKK — a designated terrorist organization that waged a three-decade insurgency inside Turkey — as more of an existential threat than ISIS, which refrained from launching attacks inside Turkey even as its militants lived and operated along the border.

"The PKK is a bigger threat to us, as it is active within the country," a Turkish official told The Wall Street Journal. "They stage attacks on our security forces on a daily basis, in many cities. ISIS is more active in Syria, and is therefore less urgent now.”

Moreover, Turkish President Recep Tayyip Erdogan's bombing campaign — capitalizing on the nationalist, anti-Kurd sentiment that has been steadily growing inside Turkey — could help him regain his AKP party's absolute majority in parliament now that coalition talks have failed and snap elections are likely.

Turkish Prime Minister Ahmet Davutoglu, also a member of the AKP, said on Thursday he would prefer an election to be held "as soon as possible", Reuters reported.

"The AKP needed the Kurdish angle to sell the war to ultranationalists inside Turkey," whose main priority is to curb Kurdish territorial gains along its southern border, Jonathan Schanzer, vice president for research at Foundation for Defense of Democracies, told Business Insider last month.

But Erdogan's gamble has come at a price: Nearly 40 Turkish police officers and military officials have been attacked and killed by PKK militants since the war began, and that number is increasing every day.

Erdogan has also complicated his party's relationship with Washington further: While the White House was relieved when Turkey announced it would allow the US to launch airstrikes against ISIS from Incirlik airbase in its southeast, the PKK is a politically contentious target.

The militia was working with US-backed Kurdish fighters to repel ISIS from northern Iraq and is also closely linked to the Kurdish YPG militia, which, backed by US airstrikes, has proved to be the most effective force fighting ISIS on the ground in northern Syria.

Now the US is reportedly embracing an all-out partnership with the YPG to make up for the failures of its $500 million Syrian train-and-equip program — a move that is sure to anger Ankara and inflame tensions even further.

"To fully embrace a Kurdish force would complicate an already fragile strategy, two [US] defense officials concluded," Nancy Youseff of The Daily Beast reports.

"The Turks ... would not welcome an emboldened Kurdish force on its southern border. Neither would many of America's Arab allies, who are also threatened by Kurdish sovereignty movements."