Imposing economic and political sanctions against Iran and North Korea will help democratic forces in those countries as Washington pursues its "ultimate objective" of regime change, John Bolton, the US ambassador to the United Nations, said on Tuesday.

Mr Bolton's comments, to Fox News, reflect the views of hardliners in the Bush administration who doubt that the threat of nuclear proliferation can be dealt with through negotiations.

Although the US denies it is pursuing a "regime change" policy towards what it calls the "axis of evil", Mr Bolton's linking of sanctions with "democratic forces" are likely to complicate delicate coalition-building efforts by Condoleezza Rice, secretary of state.

Last week Ms Rice went to Japan, South Korea, China and Russia to co-ordinate the implementation of UN sanctions imposed against North Korea in response to its underground nuclear weapon test. This week the focus shifts to New York where the US and Europe are working on a sanctions resolution for Iran.

European diplomats said they had clashed with Mr Bolton, rejecting his attempt to include a provision that would stop Russia supplying nuclear fuel to the Iranian reactor under construction at Bushehr.

Some European officials suggested Mr Bolton was "freelancing" and did not have the backing of Washington for a position that was sure to antagonise Russia. Diplomats said France, Germany and the UK would put forward a narrowly focused draft resolution soon. US officials declined to comment.

Asked by Fox News why the UN did not try to encourage political change in Iran and North Korea, Mr Bolton said talk of changing authoritarian regimes into democracies would "make a lot of countries unhappy".

He went on: "But I think that's something the United States and its friends should be pursuing on their own, because that is our ultimate objective. If you had countries that were responsive to the public will – unlike, say, North Korea or Iran – I think the odds are considerably reduced that they'd want to spend their scarce resources on nuclear weapons."

The US, he said, wanted to mobilise international support to isolate those regimes economically and politically. "That puts pressure on them internally. I think that helps democratic forces in those countries or in their diasporas."

But he also suggested that change would not happen soon.

Analysts in Tehran say his remarks will not encourage Iran to resume talks under the US-imposed precondition that it first suspend its uranium enrichment programme.

The US expressed concern that Iran will start up a second set of enrichment centrifuges at its Natanz plant in defiance of a UN demand for suspension. Iran insists it will only enrich the fuel, under international inspection, to the low level needed for a civilian reactor.