"The agreement has put us on a stronger footing as Koidu Holdings was having 70 percent of the share of benefits while the government had only 30 percent," Mining Minister Alpha Kanu said.

"But the new agreement will allow the government to realize a 60 percent share of all net benefits," he said.

Government will receive an additional 18 million dollars (14 million euro) a year as part of the new agreement under which Koidu will also provide 100,000 dollars annually to train Sierra Leoneans.

Rent has also increased from 50,000 US dollars to 200,000 dollars a year.

The review is part of a promise the government made when taking office in 2007, in an effort to improve profits from mining.

The minister said royalties for all mining companies had been increased from three percent to 6.5 percent and export duties from four percent to five percent.

Koidu Holdings is owned by a private international investment group BSG Resources Limited which has offices in London and Johannesburg.

According to Kanu an average of 10 million dollars worth of diamonds were exported into Sierra Leone per month in the first half of 2010.

The mineral-rich west African nation has worked hard to clean up its diamond industry after illegal trading of conflict-funding "blood diamonds" fueled a decade-long civil war which ended in 2002.