DR Congo security forces remain on high alert after gunmen attacked military bases in the capital, Kinshasa, on Sunday morning.
Captives were presented to the press, but it is unclear who they are
A government spokesman told AFP news agency that the attacks were an attempt to destabilise the country.
But he said it was "too early to say" whether it was an attempted coup.
The authorities have arrested at least 15 suspected attackers - said to be members of the former guard of the country's late ruler, Mobutu Sese Seko.
Some 18 others are believed to be still on the run.
A special cabinet meeting has been called to discuss the attacks, in which two government soldiers were killed and several injured.
The country's president, Joseph Kabila, called for vigilance and said the armed forces had received "precise instructions" to protect the population.
On national television late on Sunday, Mr Kabila appealed for calm and asked Congolese to "go about their daily business" and said he would appreciate the support of the population in finding hidden weapons stashes in Kinshasa.
Accusations and denials
One officer said some of the assailants came overnight from Brazzaville, the capital of the neighbouring Congo Republic across the Congo river.
More than 3,000 members of the former guard are currently housed in Brazzaville.
The authorities have since closed the border, but have not made official accusations.
The information minister of the Congo Republic, Alain Akouala, flatly denied that any of the attackers came from his country.
"Our country has nothing to do with what just happened in Kinshasa," he said.
He added that Congo-Brazzaville had bolstered security along the river to
prevent the attackers from trying to cross the border.
DR Congo - formerly known as Zaire - is emerging from five years of war in which it is thought more than three million people died.
President Joseph Kabila heads a power-sharing government under peace deals that ended the fighting in December 2002.
The transitional government is supposed to make way for a democratically elected government to be chosen in June 2005.
The BBC's Arnaud Zajtman in Kinshasa says this is the first time since beginning of the war that fighting has broken out in the heart of the capital.
The power-sharing government now has more challenges ahead, he says.