The three were convicted of terrorist-related charges in November after sharing an SMS on the Nigeria-based militant group Boko Haram which they told the court was meant to be amusing.

Rights group Amnesty collected 310,000 letters and petitions urging President Paul Biya to free them and had been intending to release the documents at a press conference.

But "early this morning, around a dozen security agents, in uniform and plain clothes, entered the hotel and ordered the managers to close the press conference venue," the group said in a statement.

"These students have done nothing more than share a private joke," said Amnesty's west and central Africa head Alioune Tine.

The students, Fomusoh Ivo Feh, Afuh Nivelle Nfor and Azah Levis Gob, have appealed their conviction for "non-denunciation of terrorism", and the hearing is set for mid June.

In late 2014, one of them received a text message from a friend saying that Boko Haram recruited young people on condition they had passed at least four exam subjects.

He sent it on, and it was eventually seen by a teacher who confiscated a phone and showed it to the police.

Cameroon is part of a regional force fighting the militants who in an eight-year campaign have killed 20,000 people and displaced millions from their homes.