A Kenyan human rights activist who exposed a secret renditions operation involving African governments and the US is to stand trial in Uganda for alleged involvement in the July suicide bombings that killed 76 people.

Al-Amin Kimathi, head of the Muslim Human Rights Forum in Kenya, was among 17 co-defendants whose cases were sent to a high court in Kampala yesterday. They have been charged with murder and terrorism related to the twin bombings in July that targeted football supporters watching the World Cup Final. The Somali Islamist group al-Shabaab claimed responsibility for the attack.

A further 17 accused were released after charges against them were dropped, although three were subsequently rearrested for separate offences.

The prosecution alleges that Kimathi provided cash used to rent a safe house in Kampala for one of the bombers before the attacks. But his lawyers say the case against him is a "fabrication", and is being used to punish him for his work defending Muslims unfairly targeted by security agencies in the region.

Local and international advocacy groups echo that view, with Human Rights Watch expressing concern that Kimathi's prosecution "is really an effort to muzzle a well-known critic of government abuses in the fight against terrorism in East Africa".

Kimathi first angered regional governments in 2007, when he lifted the lid on a clandestine operation that saw dozens of men, women and children who crossed the border from Somalia into Kenya sent back to Mogadishu and then on to secret detention centres in Ethiopia, where they were interrogated about alleged links to al-Qaida. Kimathi has since had several run-ins with the Kenyan government over the treatment of Muslims by police.

Immediately after the Kampala bombings, Kimathi issued a statement condemning the "heinous, barbaric and senseless murder of innocent people".

But he soon grew concerned by the response of security forces, especially in Kenya, where eight Muslims were detained for alleged involvement in the attacks and driven to Kampala, where they were handed to police. No judicial process was followed in Kenya, and the high court in Nairobi later ruled the renditions were illegal.

Together with Mbugua Mureithi, lawyer for the Muslim Human Rights Forum, Kimathi travelled to Kampala to assist the men. Mureithi said on 15 September he and Kimathi were lured to a hotel by members of Uganda's elite rapid response unit. With police shouting "Al-Qaeda! Al-Shabaab!", the men were bundled into the back of a van, blindfolded and shackled, and driven around the countryside for most of the next 24 hours.

They were then interrogated by Ugandan and Kenyan intelligence officers. Mureithi said an American man was also present, though not directly involved in questioning. Other people arrested in connection with the bombing claimed to have been interrogated by the American, Mureithi said. The US openly assisted the Ugandan authorities in the investigation into the bombings because an American was killed in the attacks.

Mureithi was released and deported after four days. He said the Ugandan authorities made it clear Kimathi was in for a long stay. "They said he was a supporter of al-Qaida. But al-Amin is not a terrorist. He just wants to ensure that the law is followed and that counterterrorism cases conform to local and international standards."