A rights group is calling on Congo's government to release youth activists who were arrested more than two weeks ago in a raid that also briefly swept up an American diplomat.

Security forces arrested several people at the end of a press conference on March 15 about a U.S.-sponsored event to encourage youths to participate in politics. The government has said the people present posed a threat to state security. The diplomat and some journalists were quickly released; activists from Senegal and Burkina Faso were deported.

Several Congolese activists remain in detention. Sylvain Lumu, their lawyer, says he has not been told how many are in detention or where they are being held.

Amnesty International launched a campaign Monday to call for their release. A parliamentary committee is also investigating.