A US resident was re-arrested in Sudan on Monday shortly after a judge ordered him to be freed after paying a fine for his role in Arab Spring-style protests, one of his lawyers said.
Judge Abaas Al-Khalifa sentenced Rudwan Daud to the several weeks he has already spent in custody but dismissed a terrorism-linked conspiracy and other charges.
"The court is satisfied with the length of time he has spent in jail," the judge said, ordering Daud to be released after paying a fine of 500 Sudanese pounds (about $100).
But during the release procedure, police handed him to state security agents, one of Daud's lawyers told AFP.
"The security took him away and we don't where they have taken him," said the lawyer.
Agents of the National Intelligence and Security Service have played a key role in suppressing the demonstrations which began in mid-June with University of Khartoum students protesting high food prices.
Daud could have been jailed for between five and 10 years if convicted on the most serious charge of involvement with a terrorist or criminal organisation.
Judge Khalifa said there was no evidence to support that or four other charges.
He convicted Daud of creating a disturbance.
"Because, when police arrested him, they found him putting gasoline on old tyres preparing them to be burned," the judge said.
The student protests led to the longest-running public challenge to the 23-year regime of President Omar al-Bashir.
After Bashir announced austerity measures, including tax hikes and an end to cheap fuel, scattered demonstrations calling for the government's downfall spread around the capital and to other parts of Sudan.
Burning tyres was a tactic of some protesters, but the demonstrations have faded during the Muslim holy month of Ramadan.
Daud smiled at the verdict, while about 100 of his supporters inside the courtroom applauded and said: "Justice lives."
One of his lawyers, Moutasem Al-Hassan, had asked the judge to consider that Daud's wife is pregnant, and that further jail time could affect the application which he has made for an American passport.
Another accused, Ahmed Ali, faced the same charges as Daud but was acquitted of them all on Monday.
Ten other people, including Daud's father and brother, were freed earlier for lack of evidence.
Daud is an activist with Girifna ("We are fed up"), a non-violent youth movement which, like its counterparts in Syria and elsewhere, has used Twitter and other social media to spread its anti-government message and support street protests.
Girifna said on its website that Daud was arrested at his home on July 3 after helping to organise a protest in his Khartoum-area neighbourhood.
Scores of peaceful protesters were arrested in the demonstrations which were repeatedly dispersed with excessive force, Amnesty International and Human Rights Watch said in a joint statement in July.
Many detainees were released after hours or days, but others were held for longer and "several have reported harsh treatment, including beatings and sleep-deprivation," the watchdogs said.
A senior official in the ruling National Congress Party described the protests as ridiculously small, linked to opposition political parties and amounting to nothing like the Arab Spring revolts that began in December 2010 against authoritarian rulers across North Africa and the Middle East.