Illegal diamond mining and logging by Liberian former rebels are undermining efforts to restore political stability there, says lobby group Global Witness.
Charles Taylor has political asylum in Nigeria
A new report says this is the result of a failure to reintegrate the rebels after a long civil war.
Global Witness names former President Charles Taylor - now exiled in Nigeria - as among the warlords who still play a role in the country's affairs.
It says Liberia needs to take steps against illegal mining and logging.
"Illegal diamond mining and logging by ex-combatants, who have held onto their wartime command structures, could threaten the peace by creating unregulated profits which could end up in the hands of warlords," Global Witness campaigner Natalie Ashworth said.
"It is also high time for Charles Taylor to face justice."
Liberian president-elect Ellen Johnson-Sirleaf - who won the country's first post-war poll - recently discussed Mr Taylor's future with Nigerian President Olusegun Obasanjo.
The BBC's Mark Doyle says that while illegal revenues can be a source of instability, mining also provides much needed employment for the ex-combatants.
There is little alternative employment for them in dysfunctional states destroyed by war, he says.
Global Witness says a United Nations-led demobilisation programme has failed to find the funds to provide enough employment opportunities for former rebels.
The lobby group also says the Liberian government and the UN Mission in Liberia have failed to assert their control over resource industries and failed to stop the illegal export of diamonds and timber to the benefit of militia groups.
UN officials in Liberia say that given the political will, it would be possible, at a relatively low cost, to police the diamond mines and forests of the country so they could be exploited in a sustainable way.
Mrs Johnson-Sirleaf, who will be inaugurated next month, says she has the will to tackle the problem.
But she lacks resources and criminal gangs still have considerable influence with many politicians in the country.