The head of the UN refugee agency in Liberia has expressed concern over the alleged "forced extradition" of 14 Ivorian refugees.
Khassim Diagne told the BBC there were among a group of 23 accused by Ivory Coast of being mercenaries.
The Liberian security forces are alleged to have handed them over to their Ivorian counterparts.
Liberia's government said it was not aware of the extraditions and would investigate.
More than 52,000 Ivorian refugees fled to Liberia following the violent 2011 electoral dispute which ended in the arrest of former President Laurent Gbagbo.
'Overnight river crossing'
The BBC's Jonathan Paye-Layleh in Liberia's capital, Monrovia, says there have been allegations that some of those living in the four camps along the border have been involved in cross-border attacks and recruiting people to fight the government of Ivorian President Alassane Ouattara.
"These are allegations and, of course, rumours; but none of this is being brought in front of a court of law and none of these people have been tried; no investigation has been carried," Mr Diagne said.
According to UNHCR's information, he said the extradition happened "in the middle of the night" on Sunday into the early hours of Monday morning.
A source in the area near border town of Harper told the BBC that UNHCR's own ferry was used without permission to take the men over the Cavalla River.
"The biggest concern of UNHCR is that under refugee law, this is forcible return," Mr Diagne told the BBC.
"And these are registered refugees who were recognised by the government of Liberia, given protection and assistance for a number of years and all of a sudden sent back without the due process of law taking place."