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 28 people have been killed and scores injured in a rush-hour car bombing targeting military personnel in Ankara, Turkey.
Ankara Governor Mehmet Kiliçer said the explosion was aimed at a convoy of military vehicles as it passed through the administrative center of the Turkish state, close to parliament, government buildings and Turkey’s military headquarters.
Deputy PM Numan Kurtulmus confirmed that the attack was carried out with a car bomb, but added that the perpetrators had not yet been identified.
“We do not yet know the perpetrators,” he told reporters.
“This attack did not only target our military personnel in those shuttles. This attack openly targets our entire nation. We condemn those who carried it out, those who instrumentalized the perpetrators, and those who gave logistical, intelligence and even political support to such attacks.”
An official at the armed forces’ general staff confirmed military buses had been the target, hit by an explosive-laden car as they waited at traffic lights.
President Recep Tayyip Erdogan said that the attack would only strengthen Turkey’s resolve against insurgents.
PM Ahmet Davutoğlu cancelled a trip to Brussels to attend a security briefing. He said the authorities were looking into information they have received about the explosion on Wednesday night, February 17.
President Recep Tayyip Erdogan issued a statement saying: “We will continue our fight against the pawns that carry out such attacks, which know no moral or humanitarian bounds, and the forces behind them with more determination every day.”
There was no immediate claim of responsibility. Security sources told Reuters that “initial signs [indicated] that militants from Turkey’s outlawed Kurdistan Workers Party (PKK) were behind the Ankara bombing on Wednesday”. This has not been confirmed.
ISIS militant group is the prime suspect in the Ankara bombings that killed at least 97 people on October 10, Turkish Prime Minister Ahmet Davutoglu has said.
No group has said it carried out the attack, but the Turkish government believes that two male suicide bombers caused the explosions.
Ankara explosions official death toll is 97, but one of the main groups at the march put the number of dead at 128.
The funerals of more of the victims are taking place on October 12.
The twin explosions ripped through a crowd of activists gathering outside Ankara’s main railway station.
They were due to take part in a rally calling for an end to the violence between Turkish government forces and the militant Kurdistan Workers’ Party (PKK).
Speaking on Turkish television, Ahmet Davutoglu said the bombings were an attempt to influence the forthcoming elections, due to take place on November 1 after a vote in June left no party able to form a government.
Many of the victims were activists of the pro-Kurdish HDP party, which says it is now considering cancelling all election rallies.
The HDP believes its delegation at the march was specifically targeted.
The party gained parliamentary seats for the first time in June’s vote, depriving President Recep Tayyip Erdogan’s governing AK Party of its majority.
On the day of the attack, the PKK unilaterally declared a ceasefire. However, this was rejected by the Turkish government, which carried out cross-border air strikes on PKK positions in southern Turkey and Iraq on the following day.
PM Ahmet Davutoglu said authorities were close to identifying one of the suicide bombers.
Some local media have implicated the brother of a man who carried out an ISIS bombing in the southern border town of Suruc in July, which killed more than 30 people.
HDP leader Selahattin Demirtas said the state had attacked the people – and that the people of Turkey should be the recipients of international condolences, not President Recep Tayyip Erdogan.
Turkey has declared three days of national mourning after two explosions at a peace rally in Ankara killed at least 95 people on October 10, the deadliest ever such attack in the country.
Ankara attack left 245 people injured, with 48 of them in a serious condition.
The government called the two explosions a “terrorist act” and angrily rejected allegations that it was to blame.
PM Ahmet Davutoglu said there was evidence that two suicide bombers had carried out the attack, which comes three weeks before a re-run of June’s inconclusive parliamentary elections.
Photo Getty Iamges
The two explosions took place near Ankara’s central train station as people gathered for a march organized by leftist groups demanding an end to the violence between the Kurdish separatist PKK militants and the Turkish government.
The blasts happened shortly after 10:00 local time as crowds gathered ahead of the rally. Amateur video footage showed a group of young people holding hands and singing, as the first blast hits.
No group has said it carried out the attack, but PM Ahmet Davutoglu suggested that Kurdish rebels or the Islamic State (ISIS) group were to blame.
According to terrorism experts, the attack is similar to one that was carried out in Suruc in southern Turkey by ISIS in July in which 30 people died.
However, the leader of the pro-Kurdish HDP party, whose members was among those attending the rally, has blamed the state and cancelled all election rallies.
The HDP has previously blamed the government for colluding in attacks on Kurdish activists, which the government denies.