FACTBOX: Turkish incursions into Northern Iraq

(Reuters) - Prime Minister Tayyip Erdogan called crisis talks to consider a cross-border military offensive into Iraq after Kurdish rebels killed a number of Turkish soldiers in an ambush on Sunday near the Iraqi border.

Here are some details about previous incursions:

* BACKGROUND:

-- The Kurdistan Workers Party (PKK or Kongra-Gel), founded in 1978 as a Marxist-Leninist insurgent group, has been fighting for an independent Kurdish state.

-- The PKK is considered a terrorist organization by the United States and the European Union. It has been blamed for the deaths of more than 30,000 people since it launched its armed struggle for an ethnic homeland in southeast Turkey in 1984.

-- Washington and Baghdad have so far failed to take action against the estimated 3,000 PKK guerrillas hiding in northern Iraq, despite repeated Turkish appeals over a number of years.

* MAJOR INCURSIONS:

* 1995:

-- Turkey mounted a six-week, 35,000-man operation into the Kurdish-held northern Iraqi regions on March 20, but failed to achieve its stated aim of clearing the area of the PKK. The offensive ended on May 2.

* 1997:

-- In May 1997, up to 10,000 troops launched a cross-border push into Kurdish-held northern Iraq, marking the beginning of a semi-permanent presence and regular operations there.

-- Turkish forces were supported by fighters of Iraq's Kurdistan Democratic Party (KDP) who Turkey said invited its troops into the region. KDP spokesmen did not confirm this.

-- On May 22, the Turkish army said it had killed 1,146 PKK rebels during the incursion and captured the Zap valley which it says was the main base for the PKK in the area. Turkey said it had withdrawn most of its forces from the area by the end of June.

-- In late September 1997, around 15,000 Turkish troops pushed into northern Iraq to fight PKK rebels, who have used bases in the area to strike into Turkey.

-- On December 5, 1997, thousands of Turkish troops backed by warplanes and heavy artillery launched a fresh drive against Kurdish guerrillas in northern Iraq. Up to 200 PKK guerrillas were said to have been killed in the two-week offensive.

* PRESSURE MOUNTS: