The 17 were handed sentences ranging from 45 days to three months, with Portuguese state news agency Lusa adding that three others were acquitted, according to VOA.

Lusa cited one of the defence lawyers as saying the judge declined to convert the jail sentences into fines and had acted "under much political pressure". The lawyer added that the defence will appeal against the ruling.

Inspired by uprisings in North Africa, the pro-democracy rally -- the third organised this year -- gathered around 200 youths and resulted in injuries to protesters, journalists and police officers during violent clashes.

Angola's National Police said they had been forced to intervene when they tried to dissuade the protesters from heading to the presidential palace and that four police officers had been injured by the throwing of heavy objects.

The country's main opposition party UNITA had called for the immediate and unconditional release of all the arrested protesters, while rights organisations, including New York-based Human Rights Watch, urged the government to stop using force against demonstrators.

Political tension is rising ahead of a general election planned for 2012 in a country which is Africa's biggest oil producer after Nigeria and where an estimated two-thirds of a population of 16.5 million people live on less than $2 per day.

Dos Santos' MPLA party, which in 2002 won the 27 year-long civil war against UNITA and then obtained 82 percent of the vote in the 2008 general election, has long been accused of mismanaging the country's oil revenues, avoiding public scrutiny and doing too little to fight corruption.