By John Pienaar BBC political correspondent

Nelson Mandela has warned President Bush that his administration risks destroying the United Nations if it attacks Iraq without international support.

BBC News has learned that Mr Mandela spoke directly to the US president to urge him to show restraint, saying a military strike would undermine the trust between America and a spectrum of international opinion.

The former South African president is an influential figure

Mr Mandela is also said to be seeking a meeting with UK Prime Minister Tony Blair to express his concerns.

Nelson Mandela is a natural ally of those who want to see the UN play a pivotal and decisive role, but he is also an iconic figure and a voice that both Mr Bush and Mr Blair will find hard to ignore.

Mounting pressure

Mr Blair's staff say there has been no request to talk to the prime minister so far, but as one official put it, he is always ready to talk to Nelson.

Mr Blair is already under heavy pressure from his colleagues in the Labour party to hold the American president in check - if he can.

According to opinion polls, a majority of British public opinion is opposed to a war against Iraq.

The direct intervention of a figure such as Nelson Mandela can only add significantly to the impression of mounting pressure.

Mr Blair arrived in the central Mozambique town of Dondo on Sunday to show support for the economic and political reforms he sees as the key to tackling the problems of the developing world.

He will take that message to the World Summit in Johannesburg, all the time hoping to regain control of his own political session.