KINSHASA, Zaire (AP) _ Soldiers firing tear gas broke up an anti-government protest march today and seized the prime minister before he could move into his new office.

Six soldiers forced Etienne Tshisekedi into a four-wheel drive vehicle and drove him away after he had arrived at the prime minister's office to assume the post to which he was named last week.

At the same time, about 10,000 Tshisekedi supporters rallied around the building after marching from Tshisekedi's home, but they were repeatedly driven back by hundreds of troops firing tear gas.

It was not immediately clear where Tshisekedi _ a longtime rival of President Mobutu Sese Seko _ had been taken.

Marchers took to the streets in defiance of Mobutu's announcement Tuesday that a nationwide state of emergency was in place and political rallies would be banned. Mobutu also appointed military governors throughout his crumbling country, the eastern third of which has fallen to Laurent Kabila's rebel army.

The announcement followed Kabila's claim earlier Tuesday that his troops were just 160 miles northeast of the capital, near Bandundu, and would press on to Kinshasa to end Mobutu's nearly 32-year dictatorship.

Defense Ministry spokesman Leon Kalima denied the rebels were near Bandundu but said a small group of Mobutu opponents in the city had circulated a statement announcing support for Kabila.

Mobutu faces pressure not just from Kabila but from Tshisekedi, whose supporters have taken to the streets daily this week.

About 500 people gathered outside Tshisekedi's Kinshasa home early today and began marching alongside two cars carrying the prime minister and aides to his office. Their numbers quickly swelled to about 2,000, and within minutes soldiers began firing volleys of tear gas that sent marchers fleeing and attacking journalists accompanying the march.

The marchers regrouped and the procession was allowed to continue under the eye of soldiers who drove alongside the protesters in armored vehicles. By the time they reached the prime minister's office, the protesters' numbers had grown to about 10,000.

Soldiers resumed firing tear gas after Tshisekedi emerged from his car, flashed a victory sign and tried to walk to his office.

Tshisekedi had planned to take over the prime minister's office and assert control over the government, despite efforts to oust him by Mobutu loyalists and other rival political forces.

Opposition to Tshisekedi grew after his unilateral decision to scrap the government and constitution and to offer Cabinet seats to Kabila's forces. Tshisekedi said the moves were aimed at speeding up progress toward long-stalled democratic reforms, but critics accused him of overstepping his authority.

Kabila rejected the offer of Cabinet seats and says he won't be satisfied until Mobutu is ousted. After taking the diamond-mining center of Mbuji-Mayi on Friday, the rebels were focusing on Zaire's second-largest city, Lubumbashi, capital of the southeastern copper- and cobalt-rich Shaba region.

The rebels, Kabila said, also will advance to Kinshasa to depose Mobutu and recover diamonds looted by retreating Zairian troops when they fled Mbuji-Mayi.

Kabila admitted that rebel troops had encountered stiff opposition from Mobutu's Presidential Guards near Lubumbashi, but he said the government soldiers ``will be defeated. There is no doubt about that.''

Lubumbashi, 950 miles southeast of Kinshasa, would be a big prize. Zaire's mining minister, Banza Mukalayi, estimates 80 percent of Zaire's $300 million in annual export earnings comes from area copper, cobalt and other minerals.

Banza, however, was only guessing at his figures. Exact numbers are hard to come by in Zaire, where top government officials are accused of siphoning off most of the wealth for themselves instead of repairing crumbling roads, building schools and hospitals, or paying civil servants.

``The fall of Lubumbashi will be a hard blow for the Zairian economy,'' Banza said.