Hours after the initial attacks, fighter jets were launched in a second round against Islamic State, while others targeted militants camps of the Kurdistan Workers Party(PKK) in northern Iraq, according to local media.

Reuters was unable to confirm the second round of strikes. An attack against PKK camps in Iraq would likely mark a major blow to Turkey's already stalled peace process with the Kurds.

Friday's operations followed a telephone conversation between Erdogan and U.S. President Barack Obama on Wednesday, and were accompanied by police raids across Turkey to detain hundreds of suspected militants, including from Kurdish groups.

Ankara said it had approved the use of its air bases by U.S. and coalition aircraft to mount strikes against Islamic State, marking a major change in policy that has long been a sore point for Washington.

Turkey has been a reluctant partner in the U.S.-led coalition against Islamic State, emphasising instead the need to oust Syrian President Bashar al-Assad and said Syrian Kurdish forces also pose a grave security threat.

Erdogan said the crack down against Islamic State would be in tandem with an attack on the PKK, which Ankara describes as a separatist organisation.

"In our phone call with Obama, we reiterated our determination in the struggle against the separatist organisation and the Islamic State," Erdogan told reporters. "We took the first step last night."

Turkey told the United Nations on Friday that it started conducting air strikes in Syriaagainst Islamic State militants because the Syrian government was neither capable or willing to tackle the radical Islamist group.

Turkey has faced increasing insecurity along its 900-km (560-mile) frontier with Syria. A cross-border firefight on Thursday between the army and Islamic State, which has seized large areas of Syria and Iraq, left five militants and one soldier dead.

Turkey has also suffered a wave of violence in its largely Kurdish southeast after a suspected Islamic State suicide bombing killed 32 people, many of them Kurds, in the town of Suruc on the Syrian border this week.

Erdogan's critics say he is more concerned with keeping Syrian Kurdish fighters in check, afraid that gains they have made against Islamic State in the Syrian civil war will embolden Turkey's own 14 million-strong Kurdish minority.

"Even though Erdogan has so far failed to achieve his goals in Syria - the overthrow of Assad - and Islamic State has become a problem, it is nevertheless a convenient instrument for him," said Halil Karaveli, managing editor of The Turkey Analyst, a policy journal.

"Now he has all the excuses he needs to go after the Kurds and also it makes him look very good in the eyes of the U.S., which will be happy that Turkey is on board in the coalition."

Opposition lawmakers from the pro-Kurdish Peoples' Democratic Party said Erdogan is intent on "obstructing" the advances made by the Syrian Kurds against Islamic State.

"The real aim of today's operations is not the Islamic State, but the democratic opposition," they said in an e-mailed statement.

News of the military operations further unnerved jittery investors, helping send the lira down nearly 4 percent on the week.

"WITHOUT DISTINCTION"

Three F-16 fighter jets took off from a base in Diyarbakir, southeastern Turkey, early on Friday and hit two Islamic State bases and one "assembly point" before returning, the prime minister's office said.

"We can't say this is the beginning of a military campaign, but certainly the policy will be more involved, active and more engaged," a Turkish government official told Reuters. "But action won't likely be taken unprompted."

Fighter jets late on Friday entered Syrian airspace to launch a fresh attack on Islamic State targets, local broadcaster NTV reported.

Dogan news agency reported that planes carried out airstrikes against PKK camps in five different areas of northern Iraq.

Police also rounded up nearly 300 people in Friday's raids against suspected Islamic State and Kurdish militants, Prime Minister Prime Minister Ahmet Davutoglu said after vowing to fight all "terrorist groups" equally.

Local media reported that helicopters and more than 5,000 officers, including special forces, were deployed in the operation. Anti-terror police raided more than 100 locations across Istanbul alone, broadcasters CNN Turk and NTV reported.

One senior official told Reuters: "This morning's air strike and operation against terrorist groups domestically are steps taken as preventive measures against a possible attack against Turkey from within or from outside ... There has been a move to active defence from passive defence."

Turkey has repeatedly said it will take any "necessary measures" to protect itself from attack by both Islamic State and Kurdish militants.

Obama and Erdogan agreed in their call on Wednesday to work together to stem the flow of foreign fighters and secure Turkey's border.

U.S. defence officials said on Thursday that Turkey had agreed to allow manned U.S. planes to stage air strikes against Islamic State militants from an air base at Incirlik, close to the Syrian border. U.S. drones are already launched from the base.

Turkey's Foreign Ministry went further on Friday, saying it had approved coalition strikes to be launched from its air bases. That would include air fields such as the one in Diyarbakir, southeast Turkey, from where it dispatched the F-16 fighters for the attack inSyria.

The ability to fly manned bombing raids out of Incirlik against targets in nearby Syriacould be a big advantage. Such flights have so far had to fly mainly from the Gulf.

Turkey's stance had frustrated some of its NATO allies, including the United States, whose priority is fighting Islamic State rather than Assad. The allies have urged Turkeyto do more to prevent its border being used as a conduit to Syria by foreign jihadists.

U.S. State Department spokesman Mark Toner said the agreement with Turkey was part of an "ongoing dialogue that we've had for many, many months now on how to address ISIL in the region and defeat and dismantle it," using an acronym sometimes used for the militant group.