BELGRADE, Yugoslavia -- The federal government mounted a heavy military presence Wednesday to prevent widespread ethnic violence in Croatia and Slovenia, a day after the republics declared independence from Yugoslavia.
The Yugoslav military sent 30 tanks and other armored vehicles into Serbian enclaves of Croatia to put down ethnic unrest in which four people were killed and 14 wounded. In Slovenia, tanks and military trucks patrolled roads and MiGs flew overhead in a show of force, but no bloodshed was reported there.
Sporadic ethnic unrest sprang up elsewhere, but there were no immediate reports of deaths in these incidents.
In the Croatian capital of Zagreb, the republic's assistant interior minister, Milan Brezak, described the situation as 'grave' and said ethnic Serbian provocateurs were responsible for the bloodshed in Serbian-dominated enclaves of Croatia.
In one incident, Croatian and rebellious Serbian officers of the republic's police force exchanged fire for six hours in the town of Glina, 30 miles southeast of Zagreb, Brezak said. The gunbattle left a Croatian officer, a Serbian officer and a civilian dead and 10 other people wounded, he said.
The federal military also increased the combat readiness in Slovenia, which borders Italy, Austria and Hungary.
In a separate incident in the village of Brsadin, one federal police officer was killed in a shootout between armed civilians, Brezak said.
Secretary of States James Baker, in a Wednesday night speech in Washington, stressed U.S. support for a united Yugoslavia and urged continued negotiation for 'greater autonomy and sovereignty for the republics.'
'We will not reward unilateral actions that preempt dialogue or the possibility of negotiated solutions,' Baker said. 'And, we will strongly oppose intimidation or the use of force.
'It is truly a powder keg situation, one that is deteriorating even as I speak.'
Witnesses reported tension at all of Yugoslavia's border checkpoints with Italy as federal troops and Slovene police squabbled over moves by the republic's government to replace Yugoslav frontier signs with Slovene postings.
No checkpoints at the Yugoslav-Italian frontier were closed, but at most of them, including the Slovene checkpoint at Lipice, about 12 miles east of the Italian port of Trieste, Yugoslav tanks and armored vehicles were deployed, and traffic was almost non-existent, witnesses said.
In another exercise of federal authority, the Yugoslav government closed all Slovenia's major airports, citing 'technical faults.' Slovene aviation officials inspected equipment at the Ljubljana, Maribor and Portoroz airports and argued that it was in perfect condition.
The tension, however, did not affect Ljubljana. By day the Slovene capital bustled, and after nightfall Republic Square was filled for an official celebration of sovereignty. Fireworks filled the sky to the sound of Beethoven's 'Ode to Joy.'
Slovene Information Minister Jelko Kacin in the Slovene capital of Ljubljana, 350 miles northwest of Belgrade, said his government sent a letter to the federal government in Belgrade warning against 'aggression,' saying it 'will oppose it with all means of the independent state.'
The letter also declared that Slovenia will not retract its declaration of independence and proposed 'immediate negotiations' on forming a loose alliance of the six Yugoslav republics.NEWLN: 1stadd stands
Slovenia and Croatia, Yugoslavia's westernmost republics, emphasized that the declarations of independence did not amount to secession but instead the beginning of an effort to turn the tight Yugoslav federation into a looser alliance.
The two republics want the federation dissolved into a common market- style association of independent states to escape perceived domination by Serbia, the largest republic with 8.5 million people.
The Marxist government of Serbia, in the east, wants to preserve the federation or redraw internal borders so all Serbs would live in one state to guarantee their political and civil rights. Serbia thus would annex Serbian-dominated enclaves in Croatia and Bosnia-Hercegovina.
About 600,000 Serbs live in Croatia and another 1.4 million live in Yugoslavia's central republic of Bosnia-Hercegovina. Annexation of these enclaves by Serbia is widely believed to mean civil war.
Ethnic tensions between Croats and Serbs, the two major groups in the six-republic federation, have intensified since the death of dictator Marshal Josip Broz Tito in 1980. Their leaders have done little to ease tensions among Yugoslavia's Christian Orthodox Serbs and 4.6 million Roman Catholic Croats.
At least 45 people have been killed in the past 10 months in violence related to ethnic tensions in Croatia, including 12 Croatian police officers shot by Serbian extremists May 2.
The Croatian and Slovene independence declarations have wide support in the two fiercely nationalistic republics. In December, nearly 90 percent of the Slovene electorate voted to become and independent state, as did more than 90 percent of voters in Croatia at a referendum on May 19.
On Tuesday night, after the two republics declared independence, the federal government of Prime Minister Ante Markovic, in an emergency session, voided their decrees and vowed to ensure peace throughout the country.
Slovenia and Croatia declared independence despite warnings from Western countries that they would not be recognized. Many Western leaders have noted that World War I was born in this ethnically unstable region.
The federal government also urged the republics of Serbia and Montenegro to lift their veto on the election of the rotating eight- member federal presidency that has left the country without a formal head of state since May 15.
Stjepan Mesic of Croatia was to have been named president for a one- year term in the leadership rotation system, but Serbia and Montenegro refused to agree, contending Mesic and the government of Croatian President Franjo Tudjman want to dissolve the federation.
In Washington, President Bush emphasized the need for 'unity and tranquility' in Yugoslavia. 'What we don't need is any more violence in the world,' he said. 'We do need more peace and tranquility and people sitting down and talking out their differences.'
And State Department spokeswoman Margaret Tutweiler said while the United States has not abandoned its stand on a united Yugoslavia, it 'strongly opposes the use or threat of force to resolve the political differences ... and calls on all parties to avoid unilateral acts and to continue dialogue.'
She said the department might issue an updated travel advisory for Yugoslavia superseding a March 14 notice urging Americans to defer all non-essential travel to that country.