By Opheera McDoom
KHARTOUM, Aug 3 (Reuters) - Northern and southern Sudanese leaders called for calm on Wednesday during a third day of clashes in the capital that have killed at least 84 people since the death of former southern rebel John Garang.
Violence in Khartoum erupted on Monday when angry southerners took to the streets after the official announcement of the death in a helicopter crash of Garang, who fought the northern government for two decades before making peace.
Some northerners responded to the looting and attacks by forming vigilante groups, roaming the streets.
Sudan is divided between an Arabised Muslim north and the largely African Christian and animist south.
The violence has raised fears that fresh north-south tensions could undermine a January peace deal between Garang's former rebel movement and the Islamic northern government, which also faces continued civil strife in its western Darfur region.
"Peace is being jeopardised in the short run," said Jan Pronk, the top U.N. envoy in Sudan.
Washington said it was deeply concerned about the violence and urged the government to take action to stop the clashes.
"The United States joins the rest of the international community in calling for the government to urgently take the additional steps that may be necessary to send a clear message to all the people of Sudan regarding its determination to halt the violence," State Department spokesman Tom Casey said.
Southerners fear the absence of Garang, who became first vice president on July 9 under the peace agreement, could weaken their hand in governing the oil-exporting nation.
The conflict in south Sudan began in 1983, aggravated when the Islamist Khartoum government tried to impose sharia, or Islamic law. Two million people died, mainly from hunger and disease.
The peace deal included giving southerners the right to vote on secession after a six-year interim period and shared out Sudan's oil wealth between north and south roughly equally.
"ENEMIES OF PEACE"
"I urge all the good people among you to bury the strife," President Omar Hassan al-Bashir said on state television.
Bashir said he had issued a decree establishing a joint committee with the Sudan People's Liberation Movement (SPLM), which Garang headed, to investigate the helicopter crash which killed him. There has been no suggestion of foul play.
Salva Kiir, who has been installed as the new head of the SPLM, echoed Bashir's call for calm in the southern settlement of New Site where he met top U.S. and South African envoys on a diplomatic push to maintain the fragile peace pact.
"Enemies of peace may want to take opportunity of this situation," Kiir said. "We are appealing to all the Sudanese people to refrain from any hostility."
Assistant Secretary of State for African Affairs Connie Newman and the U.S. special envoy to Sudan, Roger Winter, met SPLM officials and are due to meet Bashir.
"We came to express our continued support for the ... peace agreement and the people of Sudan," Newman said.
The violence was the worst in Khartoum in years. But many streets in the capital had emptied, except for police and soldiers on patrol, as a 9 p.m. (1800 GMT) curfew was enforced.
MOSQUES UNDER CONTROL
Khartoum's governor said more than 500 people had been arrested in the city in the past days and said the authorities were now sure they had all the mosques where incitement had taken place under control.
"Security is a gradual process, a build up," he told reporters. "You cannot just immediately expect 20,000 police to be deployed on the streets."
In a tit-for-tat attack, southern Sudanese killed the imam of a mosque in the capital's Kalakla suburb, a U.N. security briefing said.
And in the south, Bolen Kenyi, editor of the Juba Post, said demonstrations had turned violent in Juba on Monday, with southerners attacking shops of northern traders.
The International Committee of the Red Cross said it counted 84 bodies in a Khartoum morgue, all killed since Monday.