The Nigerian secret police released labor union leader Joe Ajaero on Tuesday after hours of interrogation over alleged terrorism financing.
Ajaero's arrest Monday sparked criticism about what critics see as a government crackdown on dissent.
Ajaero, was released by the Department of State Services, or DSS, after he was arrested at the Abuja airport while on his way to the United Kingdom to attend a labor conference.
He said Tuesday that DSS kept his passport.
He said the police questioned him for hours about alleged terrorism financing involving British national Andrew Wynne and last month's anti-government protests in Nigeria.
Ajaero is a prominent critic of the Nigerian government and has led many demonstrations to denounce reforms introduced by President Bola Tinubu last year.
Hamisu Santuraki, the spokesperson of the United Action Front of Civil Society, a coalition of civil society groups, said the government should have asked Ajaero to come in for questioning.
"It’s not done anywhere — arresting somebody without sending him an invitation, it is wrong, they should've sent him a letter," Santuraki said. We just want them to release his passport, so we're having a meeting. Nigeria is our country."
Later Tuesday, a government spokesman, Bayo Onanuga, said Ajaero was invited to speak to a law enforcement agency and was stopped from traveling abroad because he “snubbed” that invitation.
In a statement released on X, Onanuga also said Nigeria "categorically denies any human rights abuse.”
Santuraki said the coalition and the Labor Congress are deciding on what steps to take.
The Nigerian government is facing a wave of criticism from rights groups who accuse it of trying to stifle dissent and free expression. Investigative journalist Isaac Bristol was recently detained on charges of leaking classified and restricted documents, sedition, and tax evasion, among other allegations.
Another journalist, David Hundeyin, was declared wanted by the police last week.
Ajaero's arrest came days after he criticized a decision by Nigerian officials to increase the gasoline price by 39 percent.
Nigerian authorities said global oil market forces determined the new pump price of refined petrol, which had more than quadrupled in Nigeria since President Tinubu scrapped fuel subsidies last year.
On Monday, the Socio-Economic Rights Accountability Project, or SERAP, said state operatives also raided their offices. The group this week called for a probe of the national oil company.
"We consider this an act of aggression, intimidation and harassment by the government, and it might not be unconnected with the statement that SERAP had issued over the weekend calling on the president to direct the NNPC to reverse the price of petroleum," said Kolawole Oluwadare, a deputy director at SERAP. "We consider this as an instance of the escalation of attacks against the civic space and this of course is not acceptable in a democracy."
Ajaero was also arrested in November by police in southeastern Imo state, moments before he was to lead a rally.