Turkey's military and Islamic State fighters have exchanged fire over the Syrian-Turkish border, killing one soldier, officials say.
Turkish forces hit back when a border post was attacked from Syria, killing one militant, the army said.
The violence comes days after 32 people were killed in a suicide attack in south-eastern Turkey blamed on IS.
Meanwhile Turkey has agreed to let the US carry out strikes against IS from its airbase at Incirlik.
US defence officials speaking on condition of anonymity confirmed that the two countries had reached agreement after months of negotiations.
In other developments on Thursday:
- A Turkish traffic policeman has been shot dead and another badly injured in the city of Diyarbakir
- Turkish security forces have arrested three people for Wednesday's killing of two policemen in the city of Celanpinar
- The military wing of the outlawed Kurdistan Workers' Party (PKK) earlier said it was behind that attack
The PKK added the Celanpinar attack was revenge for the suicide bombing in Suruc, in the Kurdish-dominated south-east, claiming the policemen had collaborated with IS.
Many in Turkey feel the government in Ankara has not done enough to support the Kurds in their fight to combat the threat of IS militants across the border in Syria - something denied by the authorities.
'All necessary measures'
Two other soldiers were injured in the border violence, Kilis governor Suleyman Tapsiz told Turkey's Anadolu news agency.
Turkey would take "all necessary measures" to protect national security following the attacks, the Prime Minister's office said.
Monday's suicide attack in Suruc, near the Syrian border, was one of the deadliest attacks in Turkey in recent years.
A 20-year-old Turkish student has been identified as the bomber.
The attacker, named by local media as Seyh Abdurrahman Alagoz, was an ethnic Kurd from Turkey's south-eastern province of Adiyaman and reportedly had links to IS militants.
Alagoz's mother told the newspaper Radikal (in Turkish) that her son was a former student at Adiyaman university who had gone "abroad" six months ago with his brother.
"I don't know what they were doing abroad, they never said. They were just telling me they were fine," Semure Alagoz said.
A senior Turkish official told Reuters that he believed the bomber had travelled to Syria last year with the help of a group linked to IS militants.
The victims were mainly university students, who were holding a news conference when an explosion ripped through the group at the Amara Cultural Centre.
They had been planning to travel to Syria to help rebuild the town of Kobane. The youngest victim was Okan Pirinc, who was 18, according to the Turkish media.
On Thursday, one IS fighter alleged to have crossed from Syria into Turkey was shot dead by the youth wing of the PKK in Istanbul.
The group said the man had travelled from Kobane to Istanbul for treatment seven months ago, and had been planning attacks in the city.