Luanda (AFP) - Police in Angola have arrested 20 people at a vigil for detained opposition activists, including rapper Luaty Beirao, who have been held without trial since June, an AFP journalist witnessed.

The incident occurred late on Monday when more than 100 people gathered at a church in the capital Luanda to demand the release of 15 activists who were detained in June and accused of seeking to overthrow the government.

They lit candles and waved signs calling for the release of the prisoners, who have been held without trial for more than three months, the maximum allowed in Angolan law.

Dozens of police turned up at the scene and dispersed the demonstration, making 20 arrests, the correspondent said.

The fate of those arrested was not immediately clear, with a senior police officer who appeared on TV on Tuesday simply repeating that such vigils were illegal.

The rapper Beirao, a key figure in Angola's opposition movement, has been on hunger strike for 23 days and his health is rapidly deteriorating, according to his lawyer.

The detained activists, who belong to a youth movement that wants President Jose Eduardo dos Santos -- in power since 1979 -- to step down, face up to 12 years in jail if convicted.

The June arrests triggered international protests, but were justified by Angola's deputy state prosecutor who accused them of planning an uprising by students and workers "with incalculable consequences".

Last week, Amnesty International came out in support of an EU parliament resolution seeking the release of jailed political prisoners and human rights defenders in Angola.

Activists like Beirao are also seeking better living conditions in Africa's second-biggest oil producer, where half the population still lives off less than $2 (1.8 euros) a day and where demonstrations are banned.