They are part of a global network extending from the desert air strips of the United Arab Emirates to the armaments factories of Bulgaria and Ukraine; from the presidential palaces of Liberia, Burkina Faso and Togo to the offices of diamond dealers in Antwerp, Bombay, Monrovia, Johannesburg and Tel Aviv.

Estimates vary as to the size of the "conflict diamonds" market. De Beers, the South African mining giant, thinks that it amounts to four per cent of world diamond production.

The US and UK governments think the figure could be significantly higher.

Whatever the real figure, international concern is growing. Last week, the United Nations security council agreed an embargo on diamonds exported from areas in Sierra Leone under the control of the RUF. The ban matches a diamond embargo imposed on the Unita rebel movement in Angola in 1998 which has had a modest effect on curbing smuggling.

Britain, which pushed for the Sierra Leone embargo, is concerned about the close relationship between Sankoh and Taylor, the former rebel turned Liberian president. Both were trained in Libya; both launched rebellions between 1989 and 1991; both their armies have co-operated extensively.

A cache of documents discovered in Sankoh's villa in early May points to links between the two men and their two armies.

The documents suggest that the RUF continued trading in illicit diamonds even after a controversial peace deal was signed last July. This deal gave Sankoh a role in the government as head of a proposed commission responsible for marketing the country's diamonds.

According to a confidential RUF report dated 27 September 1999, one of the movement's commanders describes how he was instructed to take diamonds to a "business associate" of Sankoh for the "procurement of military equipment".

A second memorandum written by Sam Bokarie, a RUF general whose nom de guerre is General Mosquito, on September 26 1999 states: "With the diamond-rich ground of Kono under our control, a mining unit was set up headed by Lt Col Kennedy who is in place to give account of all proceeds from mining operations."

In June 1998 the UN security council banned the provision of "arms and related material" to non-governmental forces in Sierra Leone, including the RUF.

Monie Captan, Liberian foreign minister, denies the government has provided weapons to the RUF in exchange for diamonds. "No one in [the] Liberian government or Charles Taylor benefits from trade in Sierra Leone diamonds. Absolutely not."

But western intelligence officials are convinced that Liberia is the RUF's principal weapons supplier as well as a sanctuary for the movement, and that Bokarie is Taylor's favourite to replace Sankoh as RUF leader.

"Taylor is an integral part of the RUF," said a western intelligence official. "There is no interest in stability in Sierra Leone."

One explanation for Taylor's determination to control Sierra Leone's diamond trade could be his need to pay for arms bought from Libya. In 1989, with the support of Muammar Gadaffi, Libyan leader, Taylor unleashed a civil war in Liberia that culminated in his election as president in 1997.

A western intelligence official said Liberian bank accounts under observation showed payments from Liberia to Libya.

The British government is so convinced about Taylor's role in Sierra Leone that last month it persuaded fellow EU governments to withhold $47m of aid to Liberia. At the time the EU "expressed deep concern that President Taylor has failed to act to prevent arms and other supplies from reaching the rebels in Sierra Leone from the territory of Liberia, that close links remain between those rebels and supporters in Liberia and that the illicit diamond trade continues through Liberia".

Diamonds have played an equally influential role in perpetuating the civil war in Angola, which boasts 10 per cent of the world's diamond reserves, including some of the best quality gem stones.

Between 1975 and 1991, Angola was a case study in superpower rivalry. The Soviet Union and Cuba supported the Marxist MPLA government in Luanda. The US and South Africa backed the Unita rebels led by Jonas Savimbi, a charismatic guerrilla fighter.

But with the end of the cold war and of apartheid, Unita lost its patrons.

Its isolation deepened when Savimbi refused to accept the results of an election in 1992 which international observers judged to be free and fair. The civil war escalated, fuelled by the proceeds from diamond sales.

Despite the UN security council imposing a ban on arms and fuel sales to Unita in 1993, Mobutu Sese Seko, then president of Zaire, funnelled weapons to Unita between 1994 and 1997. He was paid in diamonds and cash.

After Mobutu was overthrown in 1997, the UN security council tried to contain the war by imposing a ban on Unita diamonds in June 1998.

But a UN report on "conflict diamonds" presented by Canadian ambassador Robert Fowler alleged that Gnassingbe Eyadema, president of Togo, became Unita's primary weapons channel.

The report also said that it was highly likely the Burkina Faso authorities had diverted weapons to Unita, and that Blaise Compaore, the country's president, had helped Unita obtain fuel.

A confidential US government report shares the conclusions about Burkina Faso and Togo. It says Unita "pays for goods with smuggled diamonds and keeps large amounts of cash stored in the residences of trusted allies".