(CNN) -- The militant fighters of the Kurdistan Workers' Party (PKK) have been engaged in a campaign of violence against the Turkish state for more than two decades with the goal of establishing an autonomous Kurdish homeland.
PKK leader Abdullah Ocalan, pictured in 1992. Ocalan is currently serving a life sentence in a Turkish prison.
The PKK accuses Turkey of oppressing Kurdish culture and suppressing Kurdish nationhood.
More than half of the world's Kurds (10 to 12 million) are estimated to live in Turkey, making up a majority in the country's south-eastern region. Iraq, Iran and Syria also have sizeable Kurdish minorities.
But the group is considered a terrorist organization by the U.S. and the European Union and is estimated to have been responsible for the deaths of more than 30,000 Turkish security force members and civilians, according to the U.S. State Department.
In 1984 the PKK launched a guerrilla struggle in response to the wave of repression that followed Turkey's military coup in 1980 when the Kurdish language and Kurdish place names banned. By then the group's founder, Abdullah Ocalan, was living in exile in Syria where he organized PKK training camps.
Since the 1980s the group has claimed responsibility for regular ambushes on military targets in the southeast but also bomb attacks across the country, notably in Turkish holiday resorts.
During the 1990s the Turkish military launched a concerted campaign to eliminate the PKK threat, adopting commando tactics and targeting the group's mountain bases.
The establishment of a "no-fly zone" over northern Iraq following the first Gulf War in 1991 also allowed Turkish troops to conduct frequent raids on PKK strongholds across the border.
In 1998, under intensive Turkish pressure, Syria expelled Ocalan and shut down the PKK camps he had established there. Ocalan was snatched by Turkish commandos a few months later while seeking asylum in Kenya.
Despite calling for a PKK cease-fire and peaceful negotiation following his capture, Ocalan was sentenced to death in 1999 following a trial condemned by the European Court of Human Rights.
However his sentence was reduced to life imprisonment when Turkey abolished the death penalty in 2002. In the same year Ocalan's brother, Osman Ocalan, who had inherited leadership of the PKK, vowed to form a new group to campaign peacefully for Kurdish rights.
But the frequency of PKK terror attacks has steadily risen since 2004 and Turkey claims the U.S.-led invasion of Iraq and the country's subsequent instability following the overthrow of the Saddam Hussein regime in 2003 has enabled the PKK to regroup.
It accuses the PKK of launching attacks on Turkish targets from secret bases in the mountainous and semi-autonomous Kurdish region of northern Iraq.
Earlier this year Turkey sent large contingents of soldiers, tanks, guns and armored personnel carriers to reinforce its frontier.
But following the deaths of 27 soldiers and 12 civilians in recent attacks, Turkish military leaders have urged the government to give them the green light to strike at PKK bases inside Iraq. E-mail to a friend