Turkish planes have for the first time carried out air strikes against Islamic State (IS) group targets in Syria.
Police also launched raids against IS and Kurdish militants across the country, arresting 251 people, the Prime Minister’s office said.
On Thursday, Turkish forces exchanged fire with IS fighters near the Syrian border. One Turkish soldier was killed.
Turkey will now let the US launch air strikes against IS from the Incirlik air base, US officials have said.
The raids in Istanbul, where 100 properties were searched, involved 5,000 officers. Members of the youth wing of the outlawed Kurdistan Workers’ Party (PKK) and of a far-left group were also arrested.
The state-run Anadolu news agency said there were also arrests in the cities of Ankara and Izmir and in Sanliurfa province, near the Syrian border.
In a separate statement, Prime Minister Ahmet Davutoglu’s office said that F-16 jets had hit three IS targets in Syria.
It is the first time Turkey has launched air raids against targets in Syria since IS began its advance through Iraq and Syria in 2013.
Turkish state TV said that the jets had not violated Syrian air space as they attacked the border town of Havar, next to the Turkish town of Kilis.
The US is expected to step up bombing raids against IS after reaching an agreement with Turkey to use the Incirlik airbase.
The agreement was finalised in a phone call between President Barack Obama and his Turkish counterpart Recep Tayyip Erdogan on Wednesday. It was confirmed by US officials speaking on condition of anonymity.
Analysis – Jim Muir, BBC News, Istanbul
Having tried somehow to keep the conflict in Syria at arm’s length despite its support for Syrian Islamist opposition groups, the proximity of the conflict and the influx of nearly two million refugees, Turkey seems now to be being drawn slowly and reluctantly into more active engagement.
Despite its status as a Nato ally, Ankara had refrained from allowing US and other coalition jets to use the big airbase at Incirlik in southern Turkey for air strikes against IS in Syria and Iraq.
Now, after months of prickly negotiations and mounting western pressure, it has relented.
After being drawn into a cross-border firefight with IS militants, it has also carried out its own air strikes against IS in northern Syria, while stressing that its jets did not violate Syrian airspace.
But it’s not just a border issue. IS militants have penetrated deep into Turkish society.
Security forces have been raiding suspected IS hideouts throughout the country, but are also after Kurdish PKK militants and radical leftists, underlining the complexity of the challenges facing the country.
The use of the Incirlik airbase broadens the US military’s ability to strike IS targets – one US official told the New York Times it was a “game changer”.
Once used in raids against former Iraqi leader Saddam Hussein, the base is near to Turkey’s long border with Syria, and significantly narrows the distance to the IS stronghold of Raqqa.
The Turkish government has faced criticism at home and abroad for not doing enough against the extremist group, despite being part of the international coalition fighting IS.
Thursday saw a deadly exchange of fire between Islamic State and Turkey near Kilis.
IS fighters attacked a Turkish border post, with Turkey’s army retaliating with heavy weaponry, killing one of the militants.
The incident comes days after the deadly bombing in the predominantly Kurdish town of Suruc, in which 32 people were killed, mostly university students.
The Turkish authorities blamed the attack on IS, with the bomber identified as a 20-year-old believed to have travelled to Syria last year with the help of an IS-linked group.
Kurdish militants said they killed two police officers in the city of Celanpinar as retaliation, accusing the policemen of having collaborated with IS.
Turkey would take “all necessary measures” to protect national security following the attacks, the prime minister’s office said.
A return to Incirlik
The US military is more than familiar with the southern Turkish base, and its recent history is tied closely with recent US military operations.
- During the first war against Iraq in 1990, US planes were stationed at the base
- Humanitarian operations for Kurdish refugees flew out of Incirlik after the war
- The base also served as the main hub for operations at the start of the war in Afghanistan in 2001
- It acted as the first stop on the way home for thousands of US troops leaving Iraq after the 2003 invasion
- Wikileaks claimed the US and Turkey allowed the base to be used to launch rendition flights for terror suspects