TUNCELI, Turkey (Reuters) - Fighting erupted Tuesday between security forces and armed rebels in a remote mountainous region in eastern Turkey, but there were no immediate reports of casualties, security officers said.

Turkish soldiers backed by warplanes and attack helicopters battled around 100 Kurdistan Workers Party (PKK) fighters and Maoist rebels belonging to the armed Turkish Workers and Peasants Liberation Army (TIKKO), an officer said.

Authorities have barred civilians from entering the area of the clashes, the former PKK stronghold of Alibogazi, a 5,000-foot-deep ravine that snakes through the Munzur Mountains in Tunceli province.

Most residents fled Alibogazi in the mid-1990s at the height of the PKK's fight for a homeland in the mainly Kurdish southeast. More than 30,000 people died in the violence.

The few remaining people dwelling on the outskirts of the valley have been ordered to remain inside their villages, the provincial governor's office said in a statement.

"Civilians have been forbidden from entering Alibogazi region for any reason (because) their lives would be at risk," the statement said.

Soldiers could mistake civilians for armed rebels in an area strewn with mines and unexploded weapons, it said.

The PKK's 17-year separatist insurgency has been reduced to sporadic clashes with the military since the 1999 capture of PKK leader Abdullah Ocalan, now on death row.

Ocalan has ordered followers to withdraw from Turkey and seek cultural rights for the country's 12 million Kurds through political channels. Ankara sees this as a ruse to make good the defeats sustained by the PKK on the battlefield.

The European Union recently added the PKK to a list of groups it considers "terrorist," prompting the PKK, which is now mainly based in northern Iraq, to change its name to KADEK.