Turkey has begun security operations against Kurdish rebels in the country’s south-east and in Iraq.
The moves come as President Recep Tayyip Erdogan vowed a crackdown on terror after Sunday’s attack in Ankara that killed at least 36 people.
A suspected bomber, who also died in the blast, was a female member of the PKK, security sources said.
Four people were held over the bombings in the south-eastern city of Sanliurfa, according to Turkish media.
Officials were quoted as saying the car used in the bombing was traced to a showroom there.
A curfew was declared in three towns in south-east Turkey, while warplanes struck PKK camps in Iraqi Kurdistan.
Eleven warplanes carried out air strikes on 18 targets including ammunition dumps and shelters in the Qandil and Gara sectors, the army said. The PKK (the outlawed Kurdistan Workers Party) confirmed the attacks.
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Tears and destruction amid PKK crackdown
Meanwhile curfews have been imposed in two mainly Kurdish towns in south-eastern Turkey, Yuksekova and Nusaybin, as security operations are carried out against Kurdish militants, Anadolu news agency reports.
Another curfew is due to start in the city of Sirnak at 23:00 local time (21:00 GMT).
No group has admitted carrying out the attack in the capital, Ankara, but government sources have cast suspicion on the PKK.
Interior Minister Efkan Ala said an investigation would conclude on Monday and those responsible would be named.
Unnamed officials said the female bomber was a member of the PKK from the eastern town of Kars who joined the group in 2013.
Kurdish rebels have carried out a series of attacks on Turkish soil in recent months, and security forces have raided Kurdish areas, after a ceasefire ended last year. The so-called Islamic State group has also targeted Ankara recently.
Turkey is part of the US-led coalition against IS and allows coalition planes to use its air base at Incirlik for raids on Iraq and Syria.
It has also been carrying out a campaign of bombardment against Syrian Kurdish fighters of the People’s Protection Units (YPG), which it regards as a extension of the PKK.
Mr Erdogan said in a statement that terror groups were targeting civilians because they were losing the battle against Turkish security forces.
Calling for national unity, he said Turkey would use its right to self-defence to prevent future attacks.
“Our people should not worry, the struggle against terrorism will for certain end in success and terrorism will be brought to its knees,” he said.
But the BBC Turkish service’s Enis Senerdem says that Ankara is the powerhouse of government and the attack sends a clear message that the establishment is under fire.
Kurdish groups across the region
- Pro-Kurdish People’s Democratic Party (HDP) – with representation in parliament but accused by ruling party of supporting militants
- Banned Kurdistan Workers’ Party (PKK) – hostile to Turkish government, has camps in northern Iraq and operates in south-eastern Turkey
- Kurdistan Freedom Hawks (TAK) – offshoot of PKK, said it was behind last month’s Ankara bombing
- Democratic Unity Party (PYD) – linked to PKK
- People’s Protection Units (YPG) – controls area on Turkish border known as Rojava. Mainly fighting IS, but regarded by Turkey as an extension of the PKK
- Kurdish Regional Government (KRG) – runs Kurdish region of northern Iraq with Peshmerga as armed forces, has friendly relations with Turkey
- KDP – dominant political party in the region
Mr Erdogan’s call for people to remain calm has not resonated, he adds.
Turkey’s pro-Kurdish political party issued a statement condemning the attack. The Peoples’ Democratic Party (HDP) said it shares “the huge pain felt along with our citizens”.
The HDP is frequently accused of being the political wing of the PKK, an accusation it denies, and of not speaking out against PKK violence.
Last month, a bomb attack on a military convoy in Ankara killed 28 people and wounded dozens more.
That bombing was claimed by a Kurdish militant group, the Kurdistan Freedom Hawks (TAK). It said on its website that the attack was in retaliation for the policies of President Erdogan.
Turkey, however, blamed a Syrian national who was a member of the YPG.
Last October, more than 100 people were killed in a double-suicide bombing at a Kurdish peace rally in Ankara.
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