UN Secretary-General Mr Kofi Annan has warned President George W. Bush that pre-emptive military intervention posed a fundamental challenge to the United Nations and could lead to a global free-for-all.
In a speech delivered shortly before Mr Bush addresses the UN General Assembly today, Mr Annan declared the Iraq crisis had brought the United Nations to a "fork in the road" as decisive as 1945 when the world body was founded.
Mr Annan questioned US arguments that nations have the "right and obligation to use force pre-emptively" against unconventional weapons systems even while they were still being developed.
"My concern is that, if it [the principle] were to be adopted, it could set precedents that resulted in a proliferation of the unilateral and lawless use of force, with or without credible justification," Mr Annan warned.
He said the UN Charter allowed military action for the purpose of self defence.
"But until now it has been understood that when states go beyond that and decide to use force to deal with broader threats to international peace and security, they need the unique legitimacy provided by the United Nations," he said.
"Now some say this understanding is no longer tenable since an 'armed attack' with weapons of mass destruction could be launched at any time," Mr Annan said.
"This logic represents a fundamental challenge to the principles, on which, however imperfectly, world peace and stability have rested for the last 58 years," Mr Annan said.
However, Annan said the 15-member Security Council, in charge of war and peace, might need to consider rewriting the rule book for the use of force.
He said he was establishing a "high-level panel of eminent personalities" to examine current challenges to peace and security and recommend ways the United Nations could reform its institutions.
Mr Annan also criticised UN members for not being able to agree on an expansion of the Security Council, which has remained nearly the same for 58 years.