The US may adjust controversial missile defence plans if Russia helps in eliminating threats from North Korea and Iran, US Under Secretary of State for Political Affairs William Burns was quoted Friday as saying.

"We hope also that Russians understand that no US president can afford a situation in which the United States is vulnerable to potential nuclear weapons on missiles from countries like North Korea or Iran," Burns told the Interfax news agency.

"And as we pursue the issue of missile defense, we obviously have to take into account a number of factors, whether the system works and whether it's cost-effective, and what's the nature of the threat," Burns said.

"If through strong diplomacy with Russia and our other partners we can reduce or eliminate that threat, it obviously shapes the way at which we look at missile defense," Burns said.

The United States has been negotiating with Poland and the Czech Republic to install 10 missile interceptors and a radar system on their territories.

The move has angered Russia as it sees the system as a threat to its security, while Washington argues the proposed shield is only directed at "rogue states," primarily Iran.

Russia had threatened to deploy Iskander missiles to Kaliningrad, a Russian enclave wedged between Poland and Lithuania, both NATO and EU members, if Washington did not halt its shield plans.

Laying out a vision of new US foreign policy, Vice President Joe Biden sought to reach out to Moscow, in a speech described by Russian Deputy Prime Minister Sergei Ivanov as positive.

Addressing the Munich Security Conference in Germany, Biden said the United States would only press ahead with its missile defence shield project "provided the technology is proven to work and cost effective," though pointing out that Washington was not shelving the plans.