A leading opponent of Liberian President George Weah on Wednesday said he had been detained in neighbouring Sierra Leone, amid allegations of passport irregularities.

Few details of the case have emerged but local media have reported that Monrovia requested opposition figure Henry Costa be extradited over problems with his travel documents.

Costa, chairman of youth activist group the Council of Patriots (COP), posted on Facebook on Wednesday that he was in the hands of Sierra Leone authorities.

“Don’t worry. I will be okay. The Sierra Leone authorities are being very professional and nice to me,” Costa said.

Local media said he was stopped from boarding a plane in Liberia on Friday for allegedly possessing forged travel documents.

Costa was meant to present himself to Liberian authorities on Wednesday, but was detained at the airport in Freetown, capital of Sierra Leone, media reported.

Liberia’s government was not immediately available for comment.

A Sierra Leone immigration official confirmed to AFP that Costa was in the country but did not comment further.

Costa is a fierce critic of footballer-turned-politician Weah and often attacks him on his popular radio show.

The president is under growing pressure to revive the West African country’s economy, which is struggling after back-to-back civil wars and the 2014-2016 Ebola crisis.

Normally resident in the United states, Costa returned to Liberia last month ahead of an anti-Weah protest which took place on January 6. (AFP)