Gunbattles erupted between Congolese security forces and armed militants who launched a series of attacks in Kinshasa on Monday, with the government reporting at least 40 assailants had been killed.
Armed youths believed to be loyal to a pastor who challenged President Joseph Kabila in elections seven years ago also stormed the state television station RTNC and took several reporters hostage.
The heavy gunfire triggered panic among residents in Kinshasa, which has mostly remained free of the conflicts that have long engulfed the mineral-rich east of the giant African nation.
Government spokesman Lambert Mende told AFP that 16 attackers had been killed at Kinshasa's international airport, 16 at the military headquarters and eight more at the RTNC premises.
The motives of the attackers were not immediately clear but Mende said the "aggression" on the eve of New Year festivities was aimed at terrorising Kinshasa citizens.
"No civilian casualties have been reported and no victims in the security forces," Mende said, adding that the assailants had yet to be identified.
A television station employee said the hostage takers had claimed loyalty to pastor Joseph Mukungubila Mutombo, one of the candidates who challenged Kabila in 2006 elections.
In an open letter dated December 5, Mukungubila expressed bitterness at the way the country was being run and showed his hate for neighbouring Rwanda, which once invaded the DR Congo and is accused by the United Nations of backing rebels.
The pastor charged that Kabila was too close to Rwanda.
Gunfire was heard near Mukungubila's residence in DR Congo's second city of Lubumbashi on Monday, according to rights group Justicia.
However, there were no reports of casualties in Lubumbashi, capital of the mineral-rich southeastern province of Katanga, and calm later returned to the area.
The US embassy said it had "received multiple reports of armed engagements and fighting around Kinshasa", together with reports of numerous military and police checkpoints and barricades.
"The embassy urges all US citizens in Kinshasa to stay in place and not travel around the city until further notice," it said in a statement.
"There's panic in the city, people are asking what is happening," a local resident told AFP, adding that he had seen police and military officers deploy around the RTNC building and the nearby parliament.
Shooting was heard near the army HQ known as the Tshatshi camp as well as the international airport at Ndjili, residents and a local journalist said.
Police officers, soldiers and Kabila's Republican Guard fanned out across the capital to restore security.
'Terror on eve of New Year festivities'
Before the RTNC television feed was cut, two young presenters were seen on screen, appearing frightened but calm, with a young man standing behind them seemingly threatening them.
The assailants "are armed with machetes and guns. They have taken reporters hostage. An operation is under way to dislodge them," police spokesman Colonel Mwana Mputu told AFP.
"We don't have the impression that the attackers had any other objective -- in such small numbers, with such weak weaponry -- but to seek... to spread panic and terror on the eve of the New Year's festivities," Mende said once the television link was restored.
He asked residents to resume their normal activities and not to worry about the security deployment.
The DR Congo is rich in a wide range of minerals, where eastern provinces have been in turmoil since even before Kabila took office in wartime in January 2001, following the assassination of his father, Laurent-Desire Kabila.
Monday's unrest comes the month after the national army, or FARDC, achieved a rare and striking military success in the strife-torn eastern North Kivu province over a powerful armed movement, the M23, which surrendered in neighbouring Uganda.
The capital has by contrast remained relatively calm, apart from an apparent coup bid in 2003 blamed by police on troops loyal to ousted dictator Mobutu Sese Seko, who was overthrown by Laurent-Desire Kabila in 1997.
The uprising was rapidly quashed.
A second coup bid attributed to renegade forces in the presidential guard took place in June 2004, but was also swiftly put down, according to the government and the large UN mission in the troubled country.
The main persistent source of trouble in Kinshasa comes from gangs of unemployed armed youths known as "kuluna" who murder, rob and assault residents.
Police in November launched a three-month operation to tackle the bandits, raising UN complaints of summary executions.