North Korea has responded angrily to a new human rights bill approved by the US House of Representatives.
By Charles Scanlon
The bill, already passed by the Senate, is designed to help North Koreans fleeing hunger and persecution.
It provides $24m a year in humanitarian assistance and also aims to make it easier for North Korean refugees to gain asylum in the US.
North Korea has said it is part of a plan to topple the communist government.
A foreign ministry spokesman in Pyongyang said the move made further negotiations with the US meaningless.
North Korea was already refusing further talks with its neighbours and the US on its development of nuclear weapons.
It has again threatened to step up development of what it calls a deterrent force, a term used to describe its nuclear weapons programme.
As many as 200,000 North Korean refugees are thought to have crossed the border into China.
The North worries that Washington is trying to encourage migration on an even larger scale to destabilise the government.
Both China and South Korea are alarmed at the prospect of a mass exodus. The Chinese authorities currently arrest and return refugees. South Korea reluctantly accepts those who manage to escape from China.