NATO's supreme commander in Europe said the alliance was very concerned about separatist moves by Croat nationalists in Bosnia and was keeping a close eye on them.
US Air Force General Joseph Ralston, on a one-day visit to Sarajevo, was due to meet peacekeeping chiefs who have faced mob attacks on their forces.
Commenting on the activity of separatists, General Ralston told reporters: "This is something that we're very concerned about...It's something that we have to pay attention to.
One central issue is arms. Peacekeepers are moving weapons to sites controlled by Croat troops loyal to the government, after soldiers and veterans supporting self-rule occupied some barracks.
A failed attempt early this month to take over a Croat-owned bank believed to be financing self-rule was the biggest humiliation suffered by peacekeepers in Bosnia since the 1992-5 war, when they were sometimes at the mercy of the warring sides.
The NATO-led Stabilisation Force (SFOR) has refused to give details of what happened, but Western diplomats say some peacekeepers were taken hostage for a few hours and others were disarmed by Croat rioters.
Twenty-two peackeepers were injured. They were forced to withdraw from several branches of the bank leaving behind valuable documentation civilian international officials needed to investigate allegations it was used to finance self-rule.
A subsequent raid last week, using much greater force and staged overnight, was much more successful, but it was not clear whether relevant documents had been removed in the interim.
Asked if any changes might be made in the peacekeeping operation as a result of the initial failure, General Ralston said: "I have to discuss this with (SFOR's commander) later today."
The rioting has fuelled discussions about whether military peacekeeping forces both in Bosnia and elsewhere in the world, such as Kosovo, are equipped to deal with outbreaks of mob violence.
"I think this was a learning experience, US Ambassador to Bosnia, Mr Thomas Miller, told a news briefing yesterday.
"The nature of the threat to stability over the past five years has changed somewhat," he said.
"The principal threat to stability now is the kind of lower intensity conflict...terrorism, car bombing, threats, intimidation, that kind of stuff," said Mr Miller, saying Croat extremists were trying to achieve their goals through violence.