(Reuters) - Angolan police arrested 18 activists staging a rare anti-government rally in the capital Luanda on Saturday, demonstration organizers said.

The protest was the first against President Jose Eduardo dos Santos - in power for 33 years - since an election last August where his MPLA party 72 percent of the vote to secure a new five-year term.

"The protest, which fulfilled all legal requirements, was the target of the usual repression by the regime, using the Angolan police," the youth protest movement Central Angola 7311 said on its Twitter feed. Two of the 18 arrested protesters were later released without charge, it said.

Calls to Angolan police for comment on Saturday went unanswered.

Saturday's protest - held near the Santa Ana cemetery, just meters away from the Luanda police command headquarters - was called to defend "the right to life and freedom of those who think differently", according to an online poster for the event.

The protesters accuse the president of mismanaging Angola's oil revenues, suppressing human rights and doing too little to end corruption and poverty.

Organizers did not say how many people were on the demonstration, but sporadic protests - which began two years ago - are usually only attended by a few dozen people.

While Dos Santos has never commented on the protests, senior members of his MPLA have accused opposition parties of planning "a national insurrection".

The U.N. Rights Committee on Thursday said it was concerned by reports of the disappearances of protesters in Luanda in 2011 and 2012 and "the reported impunity of security forces involved in such human rights violations".

Two organizers of a protest by former presidential guards, have been missing since a rally last May.

(Reporting by Shrikesh Laxmidas; Editing by Andrew Heavens)