FACTBOX: Turkish incursions into northern Iraq

(Reuters) - Turkey's military said on Friday it had launched a cross-border land offensive into northern Iraq on Thursday, backed by fighter aircraft, to hunt down Kurdish PKK guerrillas who have moved from Turkey to bases in Iraq.

Here are some details of previous Turkish incursions into Iraq against Kurdish rebels:

* BACKGROUND:

-- The Kurdistan Workers Party (PKK or Kongra-Gel), founded in 1978 as a Marxist-Leninist insurgent group.

-- The PKK is considered a terrorist organization by the United States and the European Union. It has been blamed for the deaths of nearly 40,000 people since it launched its armed struggle for an ethnic homeland in southeast Turkey in 1984.

-- Washington and Baghdad have taken no action against the estimated 3,000 PKK guerrillas hiding in northern Iraq, despite repeated Turkish appeals.

* PRESSURE MOUNTS:

-- Turkey's government has come under public pressure to act because PKK attacks from bases in northern Iraq have killed scores of Turkish troops.

-- It has sent 100,000 troops to the border and carried out a series of small bombing and ground raids, despite U.S. worries that this could destabilize northern Iraq.

* MAJOR INCURSIONS:

* 1995:

-- Turkey mounted a six-week, 35,000-man operation into Kurdish-held northern Iraq 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, the start of regular operations and a semi-permanent presence there.

-- Turkey said Iraq's Kurdistan Democratic Party invited its troops into the region and KDP fighters supported the Turkish forces. 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 PKK base. Turkey said it had withdrawn most of its forces by the end of June.

-- In late September, around 15,000 Turkish troops pushed into northern Iraq to fight PKK rebels.

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

* 2007:

-- On December 1 Turkey said it inflicted heavy casualties on Kurdish rebels in northern Iraq in an "intense intervention" involving helicopters, artillery and a cross-border raid by special forces. A PKK official said there had been no incursion.

-- On December 18 some 300 Turkish troops crossed into Kurdish territory in Dahuk, one of three mountainous Kurdish provinces in northern Iraq, to carry out a small-scale operation.

* 2008:

-- Turkey launches a cross-border land offensive backed by fighter jets on February 21 involving around 10,000 troops.

(Writing by David Cutler, London Editorial Reference Unit)