A U.N. convoy headed Wednesday for Bosnia's hungry northwest, testing Serb promises of unhindered passage in the region, where government forces have made sizable gains.

U.N. aid agency spokesman Kris Janowski said the 10-truck convoy carrying 94 tons of aid had entered territories controlled by rebel Serbs in Croatia. Other U.N. officials said a second convoy, resupplying U.N. peacekeepers in the northwestern Bihac pocket, also had moved into Serb-held lands.In the past month, Croatian Serbs and renegade Bosnian Muslims allied with Bosnian Serbs have been clashing with government troops in the northwestern Bihac pocket, which borders on Croatia.

The Croatian Serbs and Muslim rebels are not parties to the Jan. 1 truce signed by Bosnian Serbs and the government, and they have repeatedly blocked aid shipments. On Tuesday, however, they gave permission for four convoys to pass.

Janowski, a spokesman for the U.N. High Commissioner for Refugees, called the permission a "breakthrough, at least on paper." But alluding to a history of promises broken throughout the 34-month-old war, he cautioned that the convoy must go through a "lot of (Serb) checkpoints ahead" before it reaches its destination.

U.N. officials are increasingly alarmed by severe food shortages in Bihac, one of six U.N.-declared "safe areas." On Tuesday, Janowski said it was the first time people in a safe area were threatened with starvation.

As the convoy inched toward the town of Cazin in the Bihac pocket, the United Nations confirmed reports of sizable government gains in the region. Croatian media reported Tuesday that the Bosnian army and allied Bosnian Croat militias had recaptured six villages near the Croatian border.

"Government forces now control around 95 percent of the safe area," said Maj. Herve Gourmelon, a U.N. spokesman. The Bihac pocket was relatively calm early Wednesday, and Gourmelon said Bosnian Serbs had pulled back from the government advance without much resistance but warned that a counteroffensive was likely soon.

Amid the seesaw battles, international efforts continued to find a permanent end to the war.

A U.S. official in Washington said Tuesday that Britain, France, Russia, Germany and the United States have approved a plan to offer Serbia a temporary lifting of U.N. economic sanctions if it recognizes the sovereignty of Bosnia, Croatia and Slovenia, all former Yugoslav republics.