(Adds Amnesty International, updates paragraphs 1, 12 & 13)
N'DJAMENA, Feb 20 A security crackdown since a bloody rebel attack on Chad's capital this month has forced half a dozen leading human rights campaigners and members of the country's Gorane tribe into hiding or exile, activists say.
The absence of rights campaigners restricts scrutiny of the crackdown by President Idriss Deby's government, which activists say has included the abduction of several prominent opposition politicians from their homes by armed men in uniform.
"We know for sure that Chadian government security forces have shown up at the houses of various human rights activists in N'Djamena," said a human rights expert with knowledge of Chad, who declined to be named for fear of reprisals.
"Nobody is there to do the work or monitor the situation. For example, there's nobody to go and count the bodies."
Pan-African human rights organisation RADDHO said in a statement on Tuesday that Chadian opposition leaders and rights campaigners had been arbitrarily detained or forced into hiding.
But Interior Minister Mahamat Ahmat Bachir, denied soldiers had visited houses of human rights activists to arrest them.
"That's not true, they are lying," he told Reuters. "We are conducting searches for hidden weapons and rebels but this is normal straight after a war."
"Members of human rights associations are still here, as are leaders of political parties. If certain activists want to stay away and cause confusion, that's their problem," Bachir said.
Oil-producing Chad has a history of abuse. A number of rights groups are active, some trying to bring exiled ex-leader Hissene Habre to trial for alleged political murders and torture during his 1982-1990 rule.
Two opposition leaders have not been heard of since they were abducted on Feb. 3. Their parties, as well as former colonial ruler France -- which rallied to Deby's support -- have asked the government to clarify their whereabouts.
The FAR/PF party of detained opposition politician Ngarlejy Yorongar denounced his detention and "assassination attempts on his close collaborators, notably his driver and members of his family" in a statement issued on Wednesday.
"Under international law, anyone held in custody is entitled to be held in a recognised placed of detention and to have access to family, lawyers and doctors," Tawanda Hondora of Britain-based Amnesty International in a statement.
Hondora said members of the Gorane ethnic group of Mahamat Nouri, leader of the UFDD faction, had fled N'Djamena -- an assertion made by other campaigners including Daniel Deuzoumbe, president of Human Rights Without Borders (DHSF) in Chad.
Speaking from abroad by telephone, Deuzoumbe said he had fled Chad. His relatives say the Chadian military has been visiting his home regularly, looking for him, he added.
"It's the first time since Deby came to power in 1990 that all leaders of these (rights) institutions have fled. It's unprecedented. It's a very sad and dramatic time," he said.
Several journalists for independent publications have fled and three newspapers have stopped printing until the government lifts a state of emergency and ends censorship. (Editing by Alistair Thomson and Elizabeth Piper)