Forty percent of Liberia's forests have been sold off in secretive and often illegal contracts, Global Witness said Tuesday, just days after the country's president announced a probe into the issuing of logging permits.

An investigation by the London-based natural resource watchdog has shown how, despite efforts to reform the country's logging sector, companies have used a legal loophole to score contracts covering a quarter of the nation's landmass.

The report comes after President Ellen Johnson Sirleaf announced on Friday an independent probe into the controversial permits, after suspending the managing director of the Forestry Development Authority, Moses Wogbeh.

"The new logging contracts termed Private Use Permits now cover 40 percent of Liberia's forests and almost half of Liberia's best intact forests," said a press release from Global Witness.

"They have given companies linked to notorious Malaysian logging giant Samling unparalleled access to some of Liberia's most pristine forests."

Samling and its subsidiaries have been involved in cases of illegal logging from Cambodia to Guyana to Papua New Guinea.

The Private Use Permits were designed to allow private land owners to cut trees on their property. But the investigation found that the 66 permits that have been issued are in fact allowing logging companies to sneak past Liberia's carefully crafted forest laws and regulations.

"Companies holding these permits are not required to log sustainably and pay little in compensation to either the Liberian government or the people who own the forests for the right to export valuable tropical timber," Global Witness said.

"Private Use Permits are great news for logging companies. They are very bad news for pretty much everybody else in Liberia," said Robert Nyahn of Save My Future Foundation, which also took part in the investigation.

Liberia's forests make up 42 percent of what is left of the Upper Guinean Rainforest -- just part of a fragmented system that once covered most of west Africa but has been reduced to 12 percent of its original reach.

Deforestation has been alarming, with 70 percent of the population involved in slash-and-burn farming, the country's Environmental Protection Agency (EPA) told AFP in 2010.

While the use of "blood diamonds" to fund wars in the region is better known, it was timber that propped up armed factions, notably those of former president Charles Taylor, during 14 years of Liberian conflict that left over 250,000 people dead from 1989 to 2003.

In the nine years since the end of the conflict the Liberian government and international partners have worked hard to reform the industry, with the United States giving $30 million to help communities manage their forest resources.

The EU and the Liberian government have also recently negotiated a trade agreement meant to ensure that Liberia provides legal timber to European markets.

United Nations sanctions on the country's timber industry were lifted in 2006 and the government issued new licences covering nine percent of the country.

Global Witness said these new contracts have failed to deliver the promised benefits to the Liberian people and that many of these companies owe significant back taxes.

Silas Siakor of Liberia's Sustainable Development Institute said recent statements by the president on the logging scandal were "promising".

"Too frequently, those who abuse Liberia's natural resources have not been held to account," he was quoted as saying in the Global Witness press statement, calling for a comprehensive independent investigation.

According to the UN Food and Agriculture Organisation's 2010 deforestation report, Africa has lost 3.4 million hectares (8.4 million acres) of forest in the past 10 years.