In northern Kosovo in particular, K-For has often been the target of violent protests by Serbs.
The latest bomb attacks on Serbs in Kosovo illustrate the problems that Nato-led forces are having keeping the lid on the continuing violence - most of it now apparently carried out by ethnic Albanian extremists.
In some cases, ethnic Albanians want revenge for the atrocities committed earlier by Serbian security forces.
But there is also a concerted campaign by Albanian extremists to drive the Serbs out altogether.
Guerrilla force
Troops of the Nato-led force K-For often escort Serbs making trips to and from Serbia, but they do not offer guaranteed protection.
In northern Kosovo in particular, K-For has often been the target of violent protests by Serbs.
However, the main threat to the territory's fragile status quo comes from the Albanian side.
Several hundred Albanian guerrillas now operate in a long stretch of the five-kilometre-wide buffer zone between Kosovo and Serbia.
From there, especially in the Presevo Valley in the south-east, they have been harrying Serbian forces and then retreating into the zone which the Serbs are forbidden to enter.
Search for stability
On Thursday, the new democratically-elected authorities in Belgrade presented to Nato a peace plan to stabilise the region.
They are offering negotiations and better treatment for Serbia's Albanian minority.
But a key proposal is to narrow or eliminate the buffer zone so that Serbian forces can regain control of villages and roads controlled by the rebels.
It is a sign of how international sympathy has shifted that Nato Secretary-General George Robertson gave a qualified welcome to the plan as a break with the past.
But Lord Robertson added that premature changes to the buffer zone risked making matters worse. They must not create a vacuum or lead to new fighting.