The rally, held in the capital Luanda on Saturday, called for the resignation of President Jose Eduardo dos Santos, who has never before faced such dissent in his 32-year-long rule of the former Portuguese colony.
Portugal’s news agency Lusa reported that clashes between youths and police at the rally had left three injured and led to the arrest of several protesters.
“(The media reports) do not match the truth, the police did not detain anyone,” the National Police said in a statement quoted by state news agency Angop.
The statement did not say whether there had been clashes or injuries.
Angolan journalist and activist Rafael Marques told Portuguese daily newspaper Publico that he had been detained with three other reporters and released about two hours later.
U.S.-funded broadcaster Voice of America reported on its website that a Human Rights Watch researcher had been “assaulted by police forces but escaped without injury”.
Political tensions are rising ahead of an election planned for late 2012 in Africa’s biggest oil producer after Nigeria, where an estimated two-thirds of a population of 16.5 million live on less than $2 per day.
Inspired by uprisings that toppled rulers in Egypt, Libya and Tunisia, the Angolan youth movement has organised six rallies this year.
Clashes at a demonstration in September led to 24 arrests and injuries to protesters, police officers and journalists.
Dos Santos has long been accused of mismanaging oil revenues, avoiding public scrutiny and doing too little to fight corruption. But he signalled last month that he would lead the party in a re-election bid.