"We call on all the legitimate defence forces to bring all its armed forces from active to a passive defence position between the 20 August to the 20 September, 2005," the statement from KONGRA-GEL, which claims to be the political arm of the banned Kurdistan Workers Party (PKK), said.
"This shall pave the way for peace and a democratic solution hence contributing to the development of (a) resolution process," it added.
The group said it was taking the "important" step, which comes amid new signs that Ankara wants tensions to cool down, to see if there was the political will to find a solution.
"We are initiating this important and crucial conflict-free concept in order to prepare the conditions for those who made efforts to resolve the question to take further practical steps, and to see whether there is a serious and sincere attitude for peace and a democratic solution to the Kurdish question by all sides," the group said.
The KONGRA-GEL announcement comes on the week after the Turkish Prime Minister Recep Tayyip Erdogan made a landmark pledge to resolve the Kurdish conflict with "more democracy".
Kurdish rebels have stepped
up their armed offensive
In Ankara, officials declined to comment on the announcement.
A senior Foreign Ministry official, who requested anonymity, said: "Those people are terrorists and it is not possible for us to qualify their actions either as positive or negative".
Return to violence
Ankara, which considers the PKK a terrorist organisation, has meticulously avoided any move that could imply accepting the group as an interlocutor.
However, the rebel group stressed that it was ready for talks.
"Those people are terrorists and it is not possible for us to qualify their actions either as positive or negative"
Turkish Foreign Ministry official
"We clearly declare that we will immediately respond to any genuine political approach that stands for a solution, and that does not aim to eliminate the other side," the group said.
The PKK, also blacklisted as a terrorist group by the US and the European Union, has stepped up violence in the past few months after it called off a truce in June 2004, on the grounds that Ankara's steps to expand Kurdish freedoms were insufficient.
About 37,000 people had died between 1984 and 1999 as the PKK led a violent armed campaign for Kurdish autonomy in Turkey's southeast.
The announcement of the truce was originally to be made at a press conference by Kurdish rebel leader and KONGRA-GEL head Zubayir Aydar, but the briefing was cancelled at the last moment because of "Turkish pressure on Belgian authorities", a source close to the Kurdish group said.
A senior Turkish diplomat told AFP on Thursday that Ankara had asked Belgium to arrest Aydar, who, according to another Kurdish source, has enjoyed political refugee status in Switzerland since 1994.