ABIDJAN (AFP) - Ivory Coast's Laurent Gbagbo desperately clung to power on Friday as explosions and gunfire rocked Abidjan as forces loyal to leader-in-waiting Alassane Ouattara closed in on his last bastion.

While the 65-year-old strongman remained silent, his whereabouts unknown, a close aide said he has no intention of giving himself up.

Internationally recognised president Ouattara's forces swept into the economic capital Thursday with little resistance from Gbagbo's army.

As the African Union joined a chorus of international calls for the long-time incumbent to step down, machinegun-fire and heavy artillery resounded in the administrative district of Plateau, shaking the walls of buildings, according to AFP journalists.

A plume of smoke rose into the sky near the presidential palace and streets were deserted as terrified residents remained indoors.

Ouattara's camp remained positive of victory, saying Gbagbo's presidential guard, the last remaining forces he can count on, could not hold out much longer.

"I don't think Laurent Gbagbo is capable of resisting for much longer with all the defections in his ranks ... he is condemned to be removed," spokeswoman Anna Ouloto told AFP.

Gbagbo's army chief of staff, General Philippe Mangou, fled with his family on Wednesday to take refuge in the South African ambassador's residence.

As fighting intensified around the presidential palace, a Swedish United Nations employee was shot and killed, "probably by a stray bullet", the Swedish foreign ministry said.

Several hundred people have been killed in the aftermath of the presidential election in November and the UN estimates a million people have fled Abidjan in recent weeks fearing a bloodbath.

Fierce fighting broke out around the perimeter of the presidential palace in the chic suburb of Cocody around 10:00 pm Thursday.

"The shooting doesn't stop. Gbagbo's men are resisting in all their positions," another Abidjan resident told AFP.

"We are hearing deafening artillery fire, RPG7s (rockets) and machine guns," he said.

French ambassador Jean-Marc Simon told AFP he had "good reason to believe" Gbagbo had left his residence and moved into the presidential palace.

Pro-Ouattara fighters poured into Abidjan on Thursday after meeting little resistance in a four-day offensive against the Gbagbo-controlled Ivory Coast army.

The political capital Yamoussoukro and the world's biggest cocoa exporting port of San Pedro fell in quick succession.

They seized the airport and the state television on Thursday night, cutting Gbagbo's key communication channels. UN troops had since taken control of the airport.

Ouattara's government on Thursday closed all land, sea and air borders to stop Gbagbo and his allies from fleeing the country, and decreed a nightly curfew from 2100 GMT to 0600 GMT until Sunday.

Around 500 foreigners had taken refuge at the headquarters of the French military force in Abidjan, French military spokesman Thierry Burkhard told AFP in Paris.

Questions remained Friday over the likelihood of Gbagbo surrendering. The 65 year old, who has refused to cede power since losing the election, has been in power since 2000.

"President Laurent Gbagbo has no intention of abdicating or giving himself up to any rebel at all," said Toussaint Alain, a close ally of Gbagbo who acts as his Europe spokesman in Paris, saying his leader was facing a "coup d'etat."

Rumours that Gbagbo would follow his army chief of staff and take refuge in the South African ambassador's home have been swiftly denied.

"This is the first time I'm hearing about that," South African foreign ministry spokesman Clayson Monyela said in Pretoria.

AU Commission Chairman Jean Ping urged Gbagbo to immediately hand over power to Ouattara "in order to shorten the suffering of the Ivorian people."

Ping said he "deeply regrets" that Gbagbo's refusal to accept international initiatives aimed at ending the crisis, "have not made it possible to speedily complete the implementation of a peaceful solution to the crisis ..."

The bloody post-election dispute has plunged the world's top cocoa producer into political and economic crisis.

"Laurent Gbagbo must step down to avoid a bloodbath. Hopefully he will or we will go and fetch him," Ouattara's prime minister Guillaume Soro told AFP in a telephone interview from Yamoussoukro.

Several international organisations have accused Gbagbo and his allies of possible crimes against humanity for atrocities commited against civilians.

The UN human rights office on Friday said it was alarmed over reports that pro-Ouattara forces were committing equally serious human rights violations.