Turkish authorities have begun security operations against the PKK members in south-eastern Turkey and in Iraq.
The moves come as President Recep Tayyip Erdogan vowed a crackdown on terror after March 13 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.
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.
No group has admitted carrying out the Ankara attack, but government sources have cast suspicion on the PKK.
Interior Minister Efkan Ala said an investigation would conclude on March 14 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. ISIS 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.
The country 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.
President Recep Tayyip 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, Recep Tayyip Erdogan said Turkey would use its right to self-defense to prevent future attacks.
At least 32 people have been killed and more than 100 injured after a car bomb exploded in Ankara, Turkey’s health ministry has said.
The explosion happened in Guven Park in the Kizilay district, a key transport hub and commercial area.
Other vehicles at the scene were reduced to burnt-out wrecks, including at least one bus.
Last month, a bomb attack on a military convoy in Ankara killed 28 people and wounded dozens more.
According to the Hurriyet newspaper, the latest blast happened at about 18:40 local time and the area was evacuated in case of a second attack. Many ambulances were at the scene, it added.
No group has yet claimed the attack. However, a security official told Reuters news agency that initial findings suggested it was the work of the outlawed Kurdistan Workers’ Party (PKK) or an affiliated group.
President Recep Tayyip Erdogan said terror groups were targeting civilians because they were losing their struggle against Turkish security forces.
Recep tayyip Erdogan said such attacks “increase our determination to fight terrorism”.
Health Minister Mehmet Muezzinoglu told a news conference that 30 people were killed at the scene and four died later in hospital, however two of the dead are believed to be the attackers. He said 125 people were being treated at several hospitals in Ankara, of whom 19 are in a critical condition.
Interior Minister Efkan Ala said the investigation would be concluded on March 14 and those behind the bombing would be named.
The ministers were speaking after an emergency security meeting called by PM Ahmet Davutoglu.
Turkey, which was the stable corner of the Middle East and the West’s crucial ally in a volatile region, is now at a dangerous moment, the prime minister adds.
Meanwhile, it has emerged that the US embassy in Ankara warned its citizens on March 11 of a “potential terrorist plot” in the city.
Last month’s 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 Recep Tayyip Erdogan.
Turkey, however, blamed a Syrian national who was a member of another Kurdish group.