Factbox-What is the PKK, the Kurdish rebel group behind bomb blast in Turkey?

ISTANBUL (Reuters) - The Kurdistan Workers Party (PKK) militant group claimed responsibility for a bomb attack in the Turkish capital Ankara, the first such attack there in years, which prompted Turkey to hit back in Iraq and at home.

Here are details on the group:

WHAT IS THE PKK?

* The PKK is a militant group founded by Abdullah Ocalan in southeast Turkey in 1978 with an ideology based on Marxist-Leninist ideas.

WHAT DOES THE GROUP WANT?

* It launched its insurgency against the Turkish state in 1984 with the initial aim of creating an independent Kurdish state. It subsequently moderated its goals to seeking greater Kurdish rights and limited autonomy in southeast Turkey.

* More than 40,000 people have been killed in the conflict, most of them militants. Much of the fighting in the past was focused in rural areas of mainly Kurdish southeast Turkey, but it has also conducted attacks in urban areas.

* The PKK is listed as a terrorist organisation by Ankara, the United States and the European Union.

WHAT IS THE 'IMMORTALS BATTALION' GROUP?

* The PKK said the Ankara attack was staged by one of its teams in a unit called the "Immortals Battalion". A PKK commander has in the past described the unit as a group of suicide bombers in sleeper cells.

WHAT IS THE GROUP'S HISTORY?

* The PKK operated in Syria until 1998 when Ocalan had to flee amid growing Turkish pressure. He was captured by Turkish special forces several months later in Kenya and sentenced to death by a Turkish court in 1999. The sentence was reduced to life imprisonment in October 2002 after Turkey abolished the death penalty and he is still imprisoned on an island near Istanbul. Fighting dwindled after Ocalan's capture, which also led to many PKK unilateral ceasefires and to the withdrawal of rebel fighters from Turkey.

* After a later flare-up in violence, Turkey and the PKK became involved in peace talks from late 2012. But that process and ceasefire collapsed in July 2015, unleashing the bloodiest period in the conflict and resulting in extensive destruction in some urban areas of southeast Turkey.

WHERE IS THE CONFLICT FOCUSED NOW?

* In recent years the conflict has moved from southeast Turkey to be focused mainly in northern Iraq, where the PKK has bases in the mountains. Turkey has dozens of outposts in Iraq territory and has launched operations against the militants there. It frequently carries out air strikes with warplanes and combat drones.

* Iraqi President Abdul-Latif Rashid said in comments aired on Monday that Iraq rejects repeated Turkish air strikes or the presence of Turkish bases in its Kurdistan region, and hopes to come to an agreement with Ankara to solve this problem.

* Turkey also targets the YPG militia in Syria, regarding it as a PKK affiliate, and has carried out cross-border operations to push the group back from its border. However the YPG is also the spearhead of the primary ally of the U.S.-led coalition against Islamic State. Washington's support for the SDF has been a source of U.S.-Turkey tension for years.

(Reporting by Daren Butler; Editing by Jonathan Spicer and Angus MacSwan)