Serbs Hit Convoy, Kill 2 U.N. Troops : Balkans: Warning fails to stem attacks on Zepa, Sarajevo. Croatia pledges military aid to Bosnians.

Bosnian Serbs attacked humanitarian convoys bound for Sarajevo late Saturday, killing two French peacekeepers and wounding three, a U.N. spokesman said.

“One French and Danish unit was deliberately attacked by fire of multiple-barreled rocket launchers, mortars and tanks from the Bosnian Serb side,” said U.N. spokesman Lt. Col. Gerard Dubois.

He said U.N. peacekeepers returned 30 rounds of 120-millimeter mortar fire at each of two Bosnian Serb mortar positions.

The Serbs resumed their attack just after midnight today and were told that a “collateral target” would be struck if the assault were continued. The attack then halted, Dubois said.

The attack came a day after the United States and European nations issued ambiguous warnings for the Serbs to halt their attacks on U.N. “safe areas.”

The warning also failed to halt the shelling in the eastern enclave of Zepa, where the Bosnia Serbs renewed their assault. And the Serbs kept up sporadic shelling of Sarajevo, firing several artillery rounds into the city center Saturday.

Tension was also high in Bihac, another “safe area” where days of fighting has killed several people, wounded scores and left thousands homeless, according to U.N. and aid officials. They reported 150 explosions Saturday in Kamanac in the Bihac area.

In other developments:

* Croatia pledged “urgent military assistance” to Bosnia, especially in the Bihac pocket, setting the stage for a wider war encompassing both republics. Croatian President Franjo Tudjman promised the aid after meeting with Bosnian President Alija Izetbegovic.

* Representatives of Islamic countries, meeting in Geneva, signaled they would send weapons to Bosnia’s Muslim-led government forces and declared the U.N. weapons embargo on the former Yugoslavia invalid. Some countries, notably Iran, reportedly have been violating the embargo for some time, but Bosnian Foreign Minister Muhamed Sacirbey said he had received specific commitments from some countries. He refused to name them.

* President Clinton met with his chief foreign policy advisers for an hour to discuss the latest Western warnings to the separatist Serbs and the possibility of taking new diplomatic steps to encourage a peace settlement between the Muslims and the Serbs.

The White House meeting followed a 16-nation conference in London on Friday that threatened a “decisive response,” including air strikes, if the Bosnian Serbs moved in on the U.N.-declared “safe area” of Gorazde. Western allies at the meeting made no mention of Zepa or the Bihac pocket, where Serb forces from Croatia have launched an offensive.

Rebel Serbs on Saturday called the Western decision pro-Muslim and noted that government forces have used “safe areas” to stage attacks on Serbs. But the criticism was softly worded, indicating that the NATO threat was not considered major by the Serbs.

Sarajevo, Tuzla, Bihac, Zepa and Gorazde are the five remaining U.N. “safe areas” in Bosnia following the Serb seizure of Srebrenica earlier this month.

Zepa has been on the verge of collapse for several days. About 16,000 Muslims are believed surrounded by separatist Serb troops in the remote mountain enclave, whose mayor said the town’s defenders were holding their lines against a fierce artillery bombardment.

“We’re still holding on,” Mayor Mehmed Hajric said, speaking over a local ham radio link.

The pledge of military aid to the Bosnian government forces from the Croatian president apparently meant Tudjman’s government felt free to attack rebel Serbs in Croatia, who have been helping Serbs across the border in Bosnia.

U.N. officials on Saturday reported a buildup of Croatian troops near a buffer zone separating them from rebel Serbs in central Croatia, across the border from Bihac.

Rebel Serbs captured nearly a third of Croatia’s territory in 1991. Croatia retook some of that territory in May, before bowing to world pressure and stopping its blitz. The pledge of aid to Bosnian forces in Bihac could allow Croatia to restart its offensive.

In Washington, White House Press Secretary Mike McCurry said Clinton’s advisers would continue meeting during the weekend to discuss whether there were ways of moving the peace process forward.

The President heard a report from Secretary of State Warren Christopher and Gen. John M. Shalikashvili, the chairman of the Joint Chiefs of Staff, on the sessions in London. Despite some ambiguity in the conference’s decision to threaten “a firm and decisive response” if the Bosnian Serbs try to overrun Gorazde, McCurry praised the conference’s work as “a fine piece of diplomacy.”

McCurry said the President and his advisers discussed an Administration campaign to head off passage in the Senate of a resolution by Majority Leader Bob Dole (R-Kan.) that would authorize the United States, under certain conditions, to break the U.N. embargo on the sale of arms to the warring factions in Bosnia.

Times staff writer Stanley Meisler in Washington contributed to this report.