Dec 1 (Reuters) - The Turkish army carried out an "intense intervention" against Kurdish rebels in northern Iraq on Saturday, sending in special forces a day after the cabinet authorised a cross-border operation.

Here are some details about previous incursions against Kurdish rebels:

* 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 organisation 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 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 Turkey said it had withdrawn most of its forces from the area by the end of June.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 Dec. 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:

-- Ankara has massed up to 100,000 troops near the border in the past month. It has also sent hundreds of anti-terrorism special forces in preparation for a possible incursion after around 50 security personnel have been killed in PKK attacks piling further pressure on Erdogan to take tough action.

-- Last month Turkey's parliament approved a resolution giving the government the legal basis to order cross-border military operations if and when it deemed this to be necessary. (Writing by David Cutler, London Editorial Reference Unit)

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