WASHINGTON — The United States on Tuesday urged Sudan to free a US permanent resident who was taken back into custody moments after a judge freed him on charges related to helping anti-government protests.

Rudwan Daud, a citizen of Sudan who lives in the western US state of Oregon with his pregnant wife, was cleared Monday by a judge in Khartoum of the most serious charges that could have put him in jail for up to 10 years.

But as he was being released on Monday, police handed Daud to state security agents who have been instrumental in suppressing protests. His whereabouts are unknown.

"We urge the government of Sudan to respect its citizen's rights, including due process," State Department spokeswoman Victoria Nuland said.

"We strongly urge the government of Sudan to honor the decision by the judge, which was rooted in Sudanese criminal law as well as established precedent, and release Daud," she said.

Daud is an activist with Girifna ("We are fed up"), a non-violent youth movement that has used Twitter and other social media to spread its anti-government message and support street protests.

Amnesty International and Human Rights Watch have accused Sudan of excessive force in putting down protests and said that several detainees have reported harsh treatment, including beatings and sleep deprivation.