"There has been no incursion by Angolan troops into Congo... by Angola in this region," Mario Augusto, the spokesperson for the foreign ministry, told AFP.
"We do not have military forces in neither the Congo nor in the Democratic Republic of Congo (DRC)," Augusto said.
Earlier in the week Congolese officials said that Angolan troops had crossed into the country on Sunday, capturing 55 soldiers in the Kimongo region the following day who were taken back to Angola.
The soldiers were eventually released on Friday.
"Our troops... have just been freed," Jacques Mouanda, a senior official from the Niari district where the incident happened, told AFP on Friday.
"We used diplomatic channels to secure their release. There were tough negotiations," he said.
The Kimongo area has long been claimed by rebels in the neighbouring Angolan exclave of Cabinda and sources in the region said Angolan troops had crossed the international border in pursuit of the insurgents.
Cabinda borders on Congo to the north and is separated from the rest of Angola to the south by a sliver of territory belonging to the Democratic Republic of Congo.
Though small, Cabinda accounts for much of Angola's oil production, which makes the country the second largest producer in sub-Saharan Africa, after Nigeria.
Cabinda rebels have been battling Angola since the southwestern African nation achieved independence from Portugal in 1975.
The Republic of Congo, Angola and the Democratic Republic of Congo have signed a non-aggression pact and, in 1997, Angolan troops helped Brazzaville's President Denis Sassou Nguesso to fight his way back to power in a civil war.