Angola on Wednesday freed four human rights activists jailed almost a year ago in the wake of a deadly militant attack on Togo's football team on the eve of the Africa Cup of Nations in January.

The four men were found guilty in August of crimes against state security over alleged links to a militant group that opened fire on a bus carrying the Togolese national squad to a match in the restive northern enclave of Cabinda.

But the ruling was found unconstitutional under a new law on crimes against state security, said the oil-rich province's attorney general, Antonio Nito.

"They are being freed because the law on crimes against state security has been adopted by the Angolan parliament and applies retroactively," Nito told AFP.

One of the activists, lawyer Francisco Luemba, confirmed he and his co-accused had been freed.

"I've just been released. We were all freed at the same time," he told AFP by telephone as he left prison to be driven home. "I spent more than 11 months in prison. I feel relieved."

The shooting, which killed two members of the Togolese delegation and injured the team's goalkeeper, was claimed by the separatist guerrilla movement Front for the Liberation of the Enclave of Cabinda (FLEC).

A total of nine people were arrested in connection with the attack, but only two of them had any direct link to the shooting, according to Human Rights Watch.

The trial of two suspects accused of participating in the attack started in Cabinda last week. They have denied any involvement.

The four activists freed Wednesday -- Luemba, university professor Belchior Lanso, Catholic priest Raul Tati and former police officer Jose Benjamin Fuca -- were arrested because they had documents about FLEC and had travelled to Paris for meetings with exiled leaders.

Luemba and Lanso's lawyer said Wednesday his clients had been treated unjustly.

"The Cabinda court found them guilty without evidence. I think the judge was guided by emotion, or by political pressure," he told AFP.

"We are going to bring a suit to demand damages and interest" for the time they spent in prison, he added.

Human Rights Watch (HRW) said Angola's government had yet to produce a "credible investigation" into the shooting, and alleged the two people currently on trial had been abused by the military while in custody.

"Almost one year since the attack against the Togo (team), nobody was held responsible for the attack," HRW Africa specialist Lisa Rimli told AFP.

She also called for the release of another activist, Andre Zeferino Puati, convicted in June under the same law used to try the four men freed Wednesday.

FLEC separatists have been fighting for Cabinda's independence for more than three decades.

Despite a peace deal in 2006, FLEC factions continue to wage low-level attacks in the province, which produces 60 percent of Angola's oil and is separated from the rest of the country by a strip of territory belonging to the Democratic Republic of the Congo.