1 Bosnian government and rival Serb forces fought heavy infantry battles near Bihac in the northwest Friday.
2 'We believe it is very serious fighting taking place adjacent to the civilian population,' said Graham Day, a U.N. spokesman. 'Both sides are struggling to take the ground on the plateau south and southwest of the town.'
3 Tensions also increased in Sarajevo, the Bosnian capital. Serbs said they would allow no aid into the city after an ethnic Serb working with the U.N. aid agency was arrested by the Bosnian government.
4 Persistent fighting in the northwest has confounded U.N. efforts to calm Bosnia and get peace talks started. It also has hampered efforts to supply food to hungry civilians.
5 Most of the fighting in the northwest has pitted Muslim-led government troops against Serbs from nearby Croatia and Muslim forces opposed to the government. Both groups are allied with the Bosnian Serbs, but did not sign a truce that took effect Jan. 1.
6 But on Thursday, Bosnian Serbs, who did sign the truce, attacked government forces at Vedro Polje, southwest of Bihac.
7 'We are very concerned by this escalation,' Day said.
8 Damir Macic, a government army spokesman reached in Bihac, said the town itself was not under fire.
9 'The suburbs are being shelled at this hour, but the center itself is safe,' Macic said.
10 The open clash between government and Serb forces, who have mostly obeyed the terms of their truce, could seriously undermine it.
11 Explosions in Sarajevo on Thursday were the worst violation yet of the truce. U.N. officials said they probably were caused by Serb shells fired at a government bunker that they said violated the established front line at the city's Jewish cemetery.
12 Despite the fighting around Bihac, a U.N. convoy carrying food and medicine reached another part of the government-held Bihac pocket Thursday. The last convoy reached the town of Cazin on Jan. 26.
13 But U.N. officials say deliveries must arrive daily to supply the tens of thousands of people dependent on food aid.
14 At the Bihac hospital, 'doctors are complaining they can't give . (patients) medicines if they cannot feed them properly,' said Jacob Effaos, a U.N. official in the region. 'The situation is really difficult. People are dying very slowly.'
15 Bosnian authorities in Bihac called the situation 'dramatic' and appealed for aid to be airdropped over the region.
16 Three of 10 trucks in Thursday's convoy remained at Velika Kladusa, stronghold of rebel Muslim leader Fikret Abdic. He has prevented previous convoys from passing, demanding 50 percent of the aid. The UNHCR refuses to give him that much.
17 The UNHCR has encountered numerous obstacles in delivering aid throughout Bosnia since the war began in April 1992.
18 It announced Friday another indefinite suspension of the airlift into Sarajevo after Bosnian Serbs refused to allow aid convoys to enter the city.
19 Storage space at the airport is limited and there is no way to transport aid to the city without passing through a Serb checkpoint.
20 The Serb blockade was apparently a response to the detention Thursday by the Bosnian government of an ethnic Serb employee of the UNHCR. That followed the detention of a Bosnian journalist by Serb police two weeks ago.

" We believe it is very serious fighting taking place adjacent to the civilian population , " said Graham Day , a U . N . spokesman . " Both sides are struggling to take the ground on the plateau south and southwest of the town . "
" Both sides are struggling to take the ground
How is ground being prevented from being taken? 