FACTBOX: Who are the PKK?

(Reuters) - U.S. President George W. Bush and Turkish Prime Minister Tayyip Erdogan meet on Monday in Washington amid Turkey's threats to launch a major military incursion into northern Iraq against Kurdish militants.

Following are some facts on the PKK, the outlawed Kurdistan Workers Party (PKK), which has been staging attacks on Turkey from across the border.

* BEGINNINGS:

-- Abdullah Ocalan founded the party in 1974 and it was formally named the Kurdistan Workers Party in 1978, a Marxist-Leninist insurgent group fighting for an independent Kurdish state.

-- It earned a reputation for ruthlessness by killing members of rival groups, Kurdish "aga" landlords and pro-government tribesmen.

* FIGHT FOR A HOMELAND:

-- The PKK took up arms against Turkey in 1984 with the aim of creating an ethnic homeland in the southeast. Nearly 40,000 people have been killed in the conflict since then.

-- Ocalan was captured and sentenced to death by a Turkish court in 1999 but the sentence was reduced to life imprisonment in October 2002 after Turkey abolished the death penalty.

-- Fighting dwindled after Ocalan's capture and it also led to a cease-fire and the withdrawal of rebel fighters from Turkey.

* A POLITICAL STRUGGLE:

-- Ocalan, after his capture, emphasized the importance of winning rights for the Kurds through political rather than armed struggle. That encouraged the rebels to establish a new political wing known as KONGRA-GEL in November 2003.

* VIOLENCE AGAIN:

-- In June 2004, the PKK announced the end of its cease-fire and told investors and tourists to stay away from Turkey.

-- In April 2006 authorities blamed the PKK for rioting between pro-Kurdish protesters and security forces in Turkey's southeast in the worst civil unrest since the mid-1990s.

* FIGHTING RESUMES:

-- Some 3,000 PKK fighters are based in northern Iraq and have attacked security and civilian targets in Turkish territory. A few thousand PKK rebels also are believed to be in Turkey.

-- The border region saw fierce fighting last week in which three soldiers and 15 militants were killed. Twelve soldiers were killed last month, greatly increasing pressure on Turkey to send troops into northern Iraq.

-- Turkey has sent 100,000 troops to the Iraqi border, ready for a possible military incursion against PKK militants.