US warplanes Wednesday carried out their first air strikes on Islamic State (IS) targets in Syria after taking off from a Turkish base, kicking off a key new phase in the campaign against the jihadists.

A US drone had last week executed a single lethal air strike against an IS target in Syria but this was the first time manned US fighter jets had carried out raids after taking off from Turkey's strategically-located Incirlik base.

Turkey is currently pressing a two-pronged "anti-terror" offensive against IS jihadists in Syria and Kurdistan Workers' Party (PKK) militants in northern Iraq and southeast Turkey following a wave of attacks inside the country.

But until now the Turkish air strikes have overwhelmingly concentrated on the separatist Kurdish rebels, to the frustration of Western commentators who want to see Turkey ramp up its involvement in the fight against IS.

Using the Incirlik base outside the city of Adana in southern Turkey drastically cuts the distance needed for the US jets to fly to northern Syria compared with other launch bases further afield in the Middle East.

"Today, the United States began flying manned counter-ISIL missions from Incirlik Air Base, Turkey. Strikes were conducted," Pentagon spokeswoman Commander Elissa Smith said.

Turkey's Dogan news agency said three US fighter jets were seen taking off from Incirlik in the evening.

Last month, Turkey agreed to open up the base to coalition planes for bombing IS targets in Syria following months of tough negotiations.

The expectation now will be that Turkish forces -- which so far have only carried out the most limited strikes against IS -- will also join in the bombing raids.

"Turkey and the United States will coordinate operations," a Turkish official said on condition of anonymity in Ankara just before the Pentagon announcement.

"From our perspective, there has been a pause right now as Americans asked to wait for coordination purposes."

Brett McGurk, deputy US envoy for the anti-IS coalition, meanwhile wrote on Twitter that he was back in Ankara for talks with Turkish officials "to advance our joint cooperation" against IS militants.

Turkish officials have indicated a major priority will be the establishment of a safe zone inside Syria free of IS jihadists where some of the 1.8 million Syrian refugees Turkey is hosting could be housed. But Washington has yet to express clear enthusiasm for the idea.

- 'No concessions' -

President Recep Tayyip Erdogan vowed there would be "no concessions" in Turkey's relentless offensive against Kurdish militants, as its southeast was hit by new deadly violence.

One Turkish soldier and two suspected PKK members were killed Wednesday in clashes in the southeast that erupted when the Kurdish rebels attacked a military post in the Diyarbakir region, the army said.

"Let me put it clearly, the operations will continue," Erdogan told local municipal chiefs at his presidential palace in Ankara.

"We will never stop in the face of all these attacks," he added.

The state-run Anatolia news agency reported over the weekend that so far 390 "terrorists" had been killed in the campaign against the PKK.

But the Kurdish rebels have hit back, leaving a 2013 truce in tatters and a peace process to end its over 30-year insurgency for autonomy and greater rights at a dead end.

According to an AFP toll, 30 members of the security forces have been killed in PKK-linked violence since the current crisis began.

In the southeastern Hakkari province, Turkish police and protesters clashed at the funeral of a senior PKK figure, Baris Tekce, who was killed in clashes a day earlier, reports said.

- Raids against IS suspects -

Turkish authorities earlier detained at least a dozen suspected IS members in coordinated dawn raids including in the capital Ankara and Istanbul, Anatolia news agency reported.

The authorities on Tuesday announced the arrests of 23 foreign nationals -- from China, Indonesia, Russia and Ukraine -- who were trying to cross into Syria to join IS via the southeastern border town of Kilis.

In Paris, a high-ranking Turkish official told reporters that Ankara had this year expelled more than 700 people who had tried to enter Syria to join IS.

Iran closed its main border crossing into Turkey after an Iranian truck was attacked after crossing over from the Islamic Republic, state television said Wednesday, without saying who was behind the violence.

Turkey still has no new government following June 7 legislative elections, which saw the ruling Justice and Development Party (AKP), founded by Erdogan, lose its overall majority.

Prime Minister Ahmet Davutoglu and the main opposition Republican People's Party (CHP) leader Kemal Kilicdaroglu are to meet Thursday for what is seen a make-or-break meeting on forming a coalition.