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NAIROBI, Kenya (AP) — A human rights group and a lawyer on Friday said Ugandan police are illegally holding two Kenyan human rights activists who went to the country to help defend suspects charged over the twin bombings that killed 76 people in the capital.

The two activists raised concerns last month that Kenyan authorities were bypassing court procedures and secretly transferring Kenyans to stand trial in Uganda over the July 11 bomb attacks that targeted large groups gathered to watch the televised World Cup final.

Al-Shabab, an al-Qaida linked Somali insurgent group, claimed responsibility for the attacks, saying they were revenge for civilians killed by shelling from the Uganda-dominated African Union peacekeeping force in Somalia.

Human Rights Watch said Al-Amin Kimathi of the Kenyan Muslim Human Rights Forum and lawyer Mbugua Mureithi have been in police custody since Wednesday, when they were arrested at the airport.

According to the rights group, the pair went to Uganda to attend the hearing of 34 people charged for allegedly taking part in the bombings.

Ugandan lawyer Ladislaus Rwakafuuzi said he was working with the two activists to defend 12 Kenyans charged with several counts of terrorism. Rwakafuuzi said he fears for his own safety after the arrest of his colleagues.

The rights group said in a statement that the pair are at risk of being tortured by the Rapid Response Unit that arrested them. They said the unit has a history of human rights abuses, including executing suspects.

Uganda's Deputy Police Spokesman Vincent Sekatte said the two were with a wanted al-Shabab militant that police had been trailing for days before the arrests.

"We arrested people holding a meeting with a wanted suspect," he said, adding that the two activists were detained for questioning.

But Ben Rawlence of Human Rights Watch said Ugandan authorities were breaking the law by holding the two men at the Rapid Response Unit headquarters, which is not recognized by law as a detention facility.

"They should either charge them in court or release them," Rawlence said.

Rona Peligal, Africa director for Human Rights Watch, said that the arrests looked like harassment of human rights defenders.

"The Ugandan police may not agree with the concerns Mureithi and Kimathi have raised about the suspects on trial, but that is no reason to lock them up," she said.

The two activists rose to prominence in 2007 when they began helping families sue the government of Kenya over detention and illegal extradition of more than 100 people who fled Somalia in 2006 and early 2007. Those arrested in the sweeps were sent from Kenya back to Somalia and then flown to Ethiopia, where they were held in secret prisons while some were interrogated by American agents.

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Associated Press writer Godfrey Olukya in Kampala, Uganda contributed to this report.