By Stuart Williams
Turkish fighter jets have bombed Islamic State targets inside Syria for the first time.
The dramatic escalation of fighting follows the killing of a Turkish soldier in cross-border clashes.
Three Turkish F-16s took off on Friday (local time) from the southeastern Turkish city of Diyarbakir in an early morning bombing raid against three IS targets, dropping four guided bombs, a statement from the prime minister's office said.
The operation came after the first major cross-border clashes between Turkey and IS jihadists on Thursday left one Turkish soldier and one militant dead, thrusting Turkey into an open conflict with the Islamists.
The bombing raid was the first by the Turkish air force on IS since the Islamists began their advance across Iraq and Syria in 2013, seizing control of swathes of territory.
It also came as Turkey, after months of negotiations, finally gave the green light for the US to use a key air base in its south for its air strikes against IS.
The decision to launch the air force operation was taken at a meeting of security officials in Ankara late on Thursday chaired by Prime Minister Ahmet Davutoglu.
"In this context ... an operation was carried out against targets belonging to Daesh inside the Syrian border," the statement said.
"Three of our F-16s hit ... three targets," it said, adding that "the government of the Turkish Republic is determined to take the necessary measures to protect national security".
The planes dropped their bombs just before 4am and all returned safely.
On Thursday, one Turkish soldier was killed and two sergeants wounded in the Kilis region by fire from IS militants on the Syrian side of the border. A jihadist was also reported dead.
Turkish tanks then responded by opening fire on IS targets in Syria.
The fighting erupted after the killing of 32 people in a suicide bombing on Monday in a Turkish town on the Syrian border that the government blamed on IS.
This sparked an upsurge in violence in Turkey's Kurdish-dominated southeast, where many accuse authorities of collaborating with IS, accusations Ankara denies.
Turkish police on Friday launched raids to arrest suspected IS members and Kurdish militants, in an apparent bid to stamp down on all sources of violence.
A total of 251 people were detained, the prime minister's office said in a statement, adding that the raids took place in 13 provinces across Turkey.
Police had raided addresses in several Istanbul districts in search of members of IS, the Kurdistan Workers Party and other militant groups.
The Dogan news agency said about 5000 police were involved in the Istanbul operation.
As well as IS and the PKK, the operation targeted suspected members of the PKK's youth wing the The Patriotic Revolutionary Youth Movement and the Marxist Revolutionary People's Liberation Party Front, Anatolia said.
Turkey has been accused of colluding with IS extremists in the hope they might prove useful in its aim of knocking out Syrian President Bashar al-Assad. Ankara has always vehemently denied the claims.