The Turkish military on Thursday pounded positions held by Islamic State (IS) militants in Syria after a Turkish soldier was killed by fire from an area controlled by the jihadists.
The clashes -- the most serious yet between the Turkish army and IS -- came after the killing of 32 people in a suicide bombing Monday, blamed on IS, sparked an upsurge in violence.
A day after the fatal shooting of two police claimed by Kurdish militants as "revenge" for the suicide bombing in the town of Suruc on the Syrian border, a policeman was shot dead in the majority Kurdish city of Diyarbakir.
The soldier was killed from fire from an area controlled by IS in Syria in the Turkish border region of Kilis, the state Anatolia news agency said.
The Dogan news agency said four soldiers had been wounded.
Turkish tanks from the fifth armoured brigade then responded by opening fire on targets controlled by IS jihadists in Syria, NTV television said, adding that one IS militant had also been killed.
Thirty-two people -- mainly young activists, one as young as 18, preparing for an aid mission to Syria -- were killed on Monday in a devastating suicide bombing in Suruc.
That attack marked the first time the government had explicitly blamed IS for a strike in the country.
It also inflamed tensions with Turkey's Kurdish minority, which is unhappy over the lack of support provided by the government to Kurdish militias fighting IS inside Syria.
Turkey has been accused of colluding in the past 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.
The military wing of the Kurdistan Workers' Party (PKK) claimed the killing of the two police in the border town of Ceylanpinar, accusing the two slain officers of collaborating with IS extremists.
Aged 24 and 25, they were given a funeral ceremony with full honours outside police headquarters in the regional centre of Sanliurfa, their coffins draped in the Turkish flag.
"The martyrs never die, the people will never be divided," dozens of police chanted, using a well known patriotic slogan.
The state Anatolia news agency said the three suspects had been arrested in early morning raids and were being questioned, without giving further details.
In the latest violence one Turkish policeman was shot dead and another badly wounded in an attack Thursday by armed men during a routine traffic check in Turkey's majority Kurdish-city of Diyarbakir, hospital sources said.
Meanwhile the Patriotic Revolutionary Youth Movement (YDG-H), seen as a youth wing of the PKK, claimed it had shot dead an alleged former IS fighter in Istanbul late Tuesday.
Turkish officials have confirmed a 20-year-old Turkish man linked to IS carried out the suicide bombing in Suruc.
Media reports named the bomber as university student Seyh Abdurrahman Alagoz from Adiyaman in southeastern Turkey.
The unrest has intensified fears that the battle raging between Islamic State (IS) jihadists and Kurds inside Syria is now spilling over onto Turkish territory.
Deputy Prime Minister Bulent Arinc said after a cabinet meeting late Tuesday that the government had discussed an "integrated system" to secure the frontier with Syria.
Turkish media reported Wednesday that the measures were set to include sending zeppelins into the air several hundred metres high to monitor the border and building a concrete border wall.
Turkey also plans to put in place two fences separated by a military patrol road at the border, complete with observation towers at some locations, the Hurriyet daily said. A moat will also be dug at some points.
Turkey has long been accused by its Western partners of failing to properly control the 911-kilometre (566-mile) frontier and even of colluding with IS, allegations it fiercely denies.
In places, the border has been marked only with a crude wire-mesh fence ridden with holes that has provided easy passage to militants and smugglers.
Turkey has so far stopped short of playing a full role in the US-led coalition assisting Kurds fighting IS militants who have taken swathes of Iraq and Syria.
However the Hurriyet daily reported on Thursday that Ankara had finally given the green light to US forces for use of the Incirlik air base in the campaign against IS in Syria.
It said that the accord was finalised in telephone talks Wednesday between President Recep Tayyip Erdogan and his US counterpart Barack Obama.
The unrest comes at a critical time for Turkey following elections in which the ruling Justice and Development Party (AKP) of Erdogan lost its overall majority in parliament for the first time since coming to power in 2002.