Angry Bosnian Serbs Order Thorough Inspection of U.N. Aid : Balkans: Decree comes after bullets were found in flour shipment. It is likely to further delay relief efforts.

Bosnian Serb leaders responded with threats and anger Friday to the discovery a day earlier of thousands of bullets in a U.N. shipment of flour to Sarajevo and ordered thorough inspection of all further aid bound for enemy territory.

The more stringent controls at rebel roadblocks are likely to further complicate and delay the massive humanitarian relief effort in the former Yugoslav federation on which 3 million war victims now depend for food and shelter.

The incident has also undermined the 12,000-troop peacekeeping mission in this war-ravaged republic and embarrassed officials of the Office of the U.N. High Commissioner for Refugees, which has staunchly denied repeated Serbian accusations that the agency smuggles weapons to Bosnian government forces.

But the scandalous discovery filmed by TV Serbia was devastatingly ill-timed for the Sarajevo leadership, which has been trying to marshal more effective help from Western countries to halt a deadly advance by Serbian rebels on the last few Muslim enclaves in eastern Bosnia.

That has raised suspicions among relief officials, as well as within the Bosnian government, that the motivation for sending ammunition in a U.N.-escorted convoy to a Muslim-held suburb might have been other than the implied attempt to help the government forces resist the Serbs’ year-old siege.

“It was clearly a setup,” one outraged U.N. official here said.

In Washington, White House spokeswoman Dee Dee Myers said of the hidden ammunition, “We’re concerned about it, but we do believe it’s an isolated incident.” It was “unfortunate,” she added.

The U.N. refugee agency’s special envoy to the former Yugoslav federation, Jose Maria Mendiluce, has been warning in recent weeks that the aid mission has mushroomed to unmanageable proportions and has complained that his agency has become “an international trucking company.”

Dozens of countries with varying allegiances to the Bosnian combatants are taking part in the military escort of aid shipments, and the agency’s packaging, loading, sorting, delivery and distribution operations are now scattered across the Balkans and at several European bases.

Ekrem Avdic, a spokesman for the Bosnian army at Tuzla’s 2nd Corps headquarters, which commands half of all pro-government troops and two-thirds of the military hardware, dismissed the highly publicized incident as “a plant of the most primitive kind.”

“The government is not that stupid. We have ways of getting ammunition without sending it on U.N. trucks through Serbian checkpoints,” said Avdic, adding that he found it curious that TV Serbia was on hand for the find.

Serbian gunmen on Thursday found 48 boxes of bullets and machine-gun rounds under flour sacks in shipping containers that have a bottom compartment. The contraband could have been loaded at any number of stages in the aid process, refugee agency spokeswoman Sylvana Foa told journalists from agency headquarters in Geneva.

Officials of both the U.N. Protection Force and the refugee agency said investigations would be made into the incident immediately.

After the ammunition cache was discovered, the self-proclaimed government of the rebel Serbian state in Bosnia fired off a letter of protest to U.N. commanders whose troops had escorted the aid convoy, to refugee agency officials responsible for managing the huge operation and to the International Committee of the Red Cross, which also takes part in the relief mission.

The letter, parts of which were carried by the state-run Tanjug news agency in Belgrade, said the Bosnian Serb leadership “has been aware for some time that (the United Nations) has been engaged in supplying arms and ammunition to the Muslim and Croatian side.”

It accused the U.N. agencies of “dishonorable acts” and threatened to arrest aid workers and impound relief goods if any arms were discovered in subsequent shipments.

The “detailed controls” of all future aid consignments ordered by the Serbian rebels in Pale are expected to further impede deliveries to Muslim areas surrounded by Serbian forces.

As the U.N. aid convoys pass through Serbian checkpoints along the hostile, 1,000-mile front line meandering through Bosnia, the goods have often been subjected to protracted searches or blocked entirely by Serbs trying to starve out Muslim civilians in order to capture their land.

Citing the discovery of the hidden ammunition, Serbian fighters on Friday turned back aid trucks from Gorazde, a hard-hit Muslim city about 50 miles south of Sarajevo.

U.N. officials had been mounting a strong campaign to protect the Muslim town of Srebrenica from what is feared to be an impending collapse before Serbian forces. But the ammunition scandal has diverted attention and likely weakened the international body’s resolve to take further steps to punish Serbian aggression.

Senior commanders for the Yugoslav peacekeeping mission that now involves nearly 30,000 foreign troops and civilians convened a meeting with Bosnian Serb military leaders in Belgrade on Friday to push for deployment of 150 Canadian troops in Srebrenica to deter a decisive attack that would end the current siege.

But the leader of the Serb nationalist forces, Gen. Ratko Mladic, categorically rejected the deployment plan, saying the foreign troops would be allowed in “over my dead body.”

More than 40,000 people--many of them refugees from other vanquished Muslim areas--are encircled in Srebrenica and fear that a final Serbian offensive is under way.

The town was reported quiet Friday, but the United Nations postponed plans to evacuate more people until today to ease the overcrowding in Tuzla, the city to which they are being taken.