Turkish fighter jets have entered Syrian airspace and launched a fresh attack on Islamic State targets - less than 24 hours after their first airborne attack on the militants.
More than 250 suspected terrorists were rounded up across the country earlier in the day.
Three F-16 jets were involved in the early morning strike which used laser-guided bombs launched from inside Turkish territory.
The attack was the first time Turkish planes have attacked the group.
Two IS headquarters and an "assembly point" were targeted near the village of Havar - but Syrian airspace was not violated, said a government official.
Tensions have increased over the past few days after IS militants fired at a Turkish border position in Kilis on Thursday, killing a soldier and wounding two others.
Turkish tanks returned fire, reportedly killing one militant.
President Recep Tayyip Erdogan said Turkey's strikes were the "first step" and that action against IS and Kurdish militant groups would continue.
He warned the groups to lay down their weapons or "face consequences" - and also confirmed he had opened up a key air base to US planes.
His comments came after a massive police operation overnight saw hundreds detained in simultaneous raids in 13 provinces.
In Istanbul, 5,000 officers backed by helicopters targeted IS suspects and militants from the outlawed PKK (Kurdistan Workers' Party).
A female suspect was killed after clashing with police when they tried to enter one house.
Members of the Marxist Revolutionary People's Liberation Party Front were also reportedly arrested.
"A total of 251 people were taken into detention (across Turkey) for belonging to terrorist groups," said a government statement.
Violence
Turkey's leaders are under pressure at home to take more action against IS following the deaths of 32 people in a suicide bombing in the southeastern city of Suruc.
The attack ramped up tensions in the Kurdish-dominated region, with some people accusing authorities there of collaborating with IS.
The murder of two police officers near the Syrian border on Wednesday was claimed by PKK militants, who said the killings were to "avenge" the Suruc bombing.
In other violence, a policeman was killed in the Kurdish-majority city of Diyarbakir on Thursday, while the PKK's youth wing claimed it had killed a former IS fighter in Istanbul on Tuesday.
Turkey's government said in a statement it was determined to take on all "terrorist" groups "without distinction".
It also agreed this week to let the US military use the Incirlik air base near the Syrian border to launch its own attacks on IS, following months of negotiations.
American planes using the base will be able to fly into IS territory far quicker than before.
President Erdogan confirmed the air base would be used within "a certain framework" and said he had told President Obama he was committed to fighting IS.
Turkey has been the entry point into Syria for hundreds of foreigners travelling to fight with Islamic State but has so far not taken part in the US-led campaign of air strikes.
