ISTANBUL, Turkey – Turkey’s massive military buildup along the border with Iraq is evident in the daily foot patrols, convoys of military vehicles and activity at air bases. But those images, a possible precursor to a cross-border offensive against Kurdish rebels, only tell part of the story.

In past months, the military has declared large regions of rugged, sparsely populated territory in eastern Turkey to be “security zones,” meaning that civilians are barred from entry. It is virtually impossible to assess what kind of military activity is going on in those areas, where rebels of the Kurdistan Workers’ Party, or PKK, might be active.

The scarcity of detail about any fighting in areas that have been sealed off by Turkish forces means the competing claims of the soldiers and the guerrillas, who invariably dispute each other’s reports of battlefield success, are one of the few sources of information.

On Friday, the military said Turkish troops killed a Kurdish rebel in the province of Bingol after he refused calls to surrender and opened fire on the troops. Separately, Dogan news agency said police in Siirt city detained four suspected rebels and seized guns and hand grenades.

On the diplomatic front, Secretary of State Condoleezza Rice met Turkish officials in Ankara in an effort to persuade them not to launch an attack on rebel bases in Iraq, and assured them of U.S. support in the fight against what she called a common enemy. Washington fears a Turkish incursion would destabilize a part of Iraq, the Kurdish-controlled north, that has escaped the kind of intense violence seen elsewhere in the country.

There have been fewer reports of fighting in recent days in southeast Turkey, where PKK guerrillas have traditionally carried out their operations. One possible explanation is that the intensity of military operations since an Oct. 21 rebel ambush that killed 12 soldiers has forced the rebels to retreat deeper into the mountains.

Aliza Marcus, author of a book titled “Blood and Belief: the PKK and the Kurdish Fight for Independence,” said it appeared that the guerrillas had adopted “a defensive posture” since the ambush near the Iraq border, in which they also abducted eight soldiers.

The rebels, who demand more rights for Turkey’s Kurdish minority, traditionally end their annual fighting season at this time of year, before winter snows make it difficult to move around in the rugged terrain. Their strength has diminished since the peak of their powers in the mid-1990s, when they set up highway checkpoints and effectively controlled many areas by night when military patrols withdrew to their barracks.

James Brandon, a London-based analyst who visited the PKK’s main base in northern Iraq last year, said the Oct. 21 attack was a boost for rebels who have taken heavy blows from the Turkish military over the years.

“These latest military encounters give the PKK the opportunity to say that they can confront the Turkish military for the first time in years on a relatively level playing field,” Brandon said.

In a rare insight into military tactics, Dogan agency reported Friday that soldiers were deployed on Gabar mountain, waiting to ambush any rebels who might try to escape there from fighting on another mountain.

Turkey said it has killed dozens of rebels in the recent fighting, but there has been no independent confirmation.