Horror in Bosnia: Children Slain as Parents Watch : Balkans: Newspaper’s account describes staple of a brutal war--civilians being slaughtered in ethnic conflicts.

“I am the extremist!” a Muslim engineer insisted to his captors, begging to be executed instead of his young son.

But armed vigilantes defending the Serb-held city of Visegrad, in Bosnia-Herzegovina, rejected the father’s desperate plea.

“No, you we will not kill,” one gunman reportedly replied. “We will kill your son and you will suffer for it.”

In a chilling account of the civilian slaughter that has become a staple of the Yugoslav war, the respected Belgrade newspaper Borba on Tuesday quoted an eyewitness relating how the engineer’s son and 16 other Muslim children were gunned down by guerrillas before their parents’ eyes.

There was also word from Bosnia on Tuesday of another armed attack on a U.N.-escorted aid convoy. Two relief workers, the latest in a growing list of volunteers maimed or killed on good Samaritan missions, were blown from their vehicles and left to bleed on the road as sniper fire prevented medics from reaching them.

Tales of horror have mounted with the intensity of war in Bosnia-Herzegovina, where at least 2,300 people, most of them Muslim civilians, have been killed as armed Serbs have ripped “ethnically pure” enclaves out of what was once a tolerant and integrated state.

A senior official from the 14,000-person U.N. peacekeeping force in Yugoslavia, civilian affairs coordinator Cedric Thornberry, traveled to Sarajevo for another attempt at negotiating safe passage for food and medicine to the Bosnian capital, where those left of the city’s 600,000 residents have been living under siege for two months.

But Muslims, Serbs and Croats braving the rain of shellfire from Serb-controlled hills surrounding the city say they have little hope that the latest diplomatic foray will be any more successful than dozens of others that failed.

“The situation is completely irrational. There are no guarantees for anyone here,” Sarajevo journalist Zlatko Dizdarevic said over the telephone from his office-turned-bunker at the newspaper Oslobodjenje.

Confirming the West’s worst suspicions of a nationalist adventure run amok, Dizdarevic said the Bosnian capital is now under fire from so many splintered and rival militias that not even the political radicals who armed them maintain any semblance of control.

“These are people from Serbia, not Serbs from Bosnia-Herzegovina,” Dizdarevic said of the attackers, claiming that virtually all of his Serbian co-workers were dug in alongside Muslims and Croats in defense of their city.

The land grab that is behind the vicious war gutting Bosnia is believed to have been initiated by Serbian President Slobodan Milosevic, who stationed more than 100,000 Yugoslav troops in the republic to help Serbian militants fight Bosnian secession.

Belgrade-based militia units also flooded into Bosnia after a Feb. 29 referendum endorsed independence. They pushed out Muslims and Croats from broad regions of the republic that Serbia needs as a land bridge to ethnic Serb enclaves seized from Croatia last year.

The Serbian assaults have sparked retaliatory actions by Muslim and Croatian forces, engulfing the republic in warfare and driving more than 1 million people from their homes.

In a report released in New York, U.N. Secretary General Boutros Boutros-Ghali said Croatian forces were instigating much of the fighting in western Herzegovina and implied that they were under the control of the nationalist regime in Zagreb, Croatia’s capital.

Serbs and Croats fought to a bloody standstill last year in Croatia, where 10,000 were killed and 700,000 made homeless. Fighting has eased since the arrival of U.N. forces. But one-third of the republic remains under Serbian control, and Croatian forces have warned they will fight to get that land back.

Seething emotions from the recent conflicts, as well as memories of ethnic atrocities committed during World War II, have inspired extremists to take advantage of the war’s victims. Serbian gunmen held 7,000 Muslim women and children hostage for three days last week in an attempt to negotiate the release of federal army cadets trapped by Bosnian government forces in Sarajevo.

Four busloads of Muslim refugees forced from the Serb-held city of Visegrad were involved in the callous attack reported by Borba. The roughly 200 civilians had been offered shelter in Macedonia, which has so far managed to stay out of the Balkan war. But soldiers refused to let the refugee convoy pass through Serbia, which lies between Bosnia and Macedonia. As the buses tried to return to Visegrad, armed men halted the convoy in the village of Bosanska Jagodina.

According to Borba, 17 children were separated from the adults and executed in punishment for what the gunmen claimed was extremist action against newly imposed Serbian rule.

Renegade militia bands are also suspected in Tuesday’s machine-gun attack on the U.N.-escorted convoy in the Sarajevo suburb of Dobrinja. Sarajevo Radio blamed the assault on Serbian fighters.

The convoy was trying to take baby food and medicine to the Bosnian capital, where many of the holdouts are said to be starving.

“There is not even food in the hospitals,” said Dizdarevic, chief of staff of Bosnia’s leading newspaper. “Those injured in last week’s massacre (when mortars killed at least 20 in a Sarajevo bread line) have gone for days with nothing but tea to sustain them after operations and amputations.”

Shelling continued Tuesday despite a U.N.-mediated cease-fire that was to have taken effect Monday night, according to those in the Bosnian capital.

Warplanes of the Yugoslav federal army attacked the city of Tuzla overnight, Sarajevo media reported. Tuzla is one of the last remaining Muslim strongholds in the northern Bosnian corridor that Serbs want to control.

Serbian and Croatian forces also exchanged gunfire near the walled city of Dubrovnik on the Adriatic Sea. It was the fifth straight day of fighting over Croatia’s most treasured resort, which suffered three months of Serbian bombardment last winter.

In an attempt to curb Serbian violence against Bosnia, the United Nations on Saturday approved the harshest sanctions ever imposed on a European country, including an oil embargo, a trade ban, severed transport links, a freeze on foreign assets and exclusion of Serbia and Montenegro from international sports events.

The sanctions are expected to have little immediate effect, although they will damage the already shattered economy in the long run.

Those huddled in basements and bomb shelters in devastated Sarajevo say they have little hope that economic measures will bring an end to their suffering.

“All this seems to be a political game between the United States and the European Community,” Dizdarevic said of the diplomatic debate over whether foreign military forces should intervene to stop the bloodshed in Bosnia. “I’m not sure we are important to anyone in the world.”