Liberia has arrested some 70 people near its southeastern border with Ivory Coast for their alleged involvement in plans to destabilise the neighbouring country, an administrative official told AFP.

"The Liberian government arrested more than 70 of these people on January 28, but a huge number of them are still hiding around," said the source, speaking on condition of anonymity from Zwedru, some 560 kilometres (350 miles) from the capital Monrovia.

"They were training and recruiting fighters to go against the government of Ivory Coast. It is difficult to control their movement because of the large and dark forest they are operating from."

A source close to the national police confirmed the information.

"Those who were arrested had a plan to destabilise Ivory Coast. You know that the government of Liberia cannot just sit and see such thing going on," he told AFP.

The administrative official said those arrested were "a mixture of ex-militias loyal to the former president of Ivory Coast (Laurent Gbagbo) and Liberian mercenaries who fought alongside them."

The United Nations and Human Rights Watch reported the presence of Liberian mercenaries in Ivory Coast where fierce battles broke out when strongman Laurent Gbagbo refused to accept defeat in November 2010 polls.

Gbagbo was captured in April and his rival Alassane Ouattara was inaugurated as president the following month.

The mercenaries, left over from Liberia's own brutal civil war which ended in 2003, were implicated in gruesome massacres in the west Ivory Coast, rape and looting.

During the heat of the Ivorian crisis, Liberian President Ellen Johnson Sirleaf warned all ex-combatants carrying out mercenary activity in Ivory Coast would be prosecuted.

Liberian police in August seized "worrisome" amounts of weapons in the counties of River Gee, Maryland, Grand Gedeh and Nimba.