MANAMA, Bahrain, Aug. 18 (UPI) -- Bahrain has arrested rights defenders, political activists and clerics in a clampdown on opposition figures before upcoming elections, a rights group says.

Amnesty International is urging Bahraini authorities to reveal the whereabouts of eight people arrested amid fears they were held only because of their beliefs, the group said in a release Wednesday.

"The Bahraini authorities must make it clear why these eight men have been arrested, and either release them or charge them with recognizable criminal offenses," said Hassiba Hadj Sahraoui, deputy director of Amnesty International's Middle East and North Africa program.

"It is unacceptable for them to be held merely because of their human rights activism, non-violent political activities or criticism of the government," Sahraoui said.

The latest arrests mark an increased clampdown on opposition and civil society activists in the lead-up to parliamentary elections in October, Amnesty International said.

Neither the families nor the legal representatives of the detainees have been informed of any formal charges, AI said.

"All of these detainees should be allowed to have immediate access to their lawyers, families and also to adequate medical care," Sahraoui said.