US Vice President Joe Biden said Saturday the United States would press ahead with its missile defence programme -- provided it works, is cost effective, and in consultation with Russia.
"Faced with new threats, we need a new resolve to meet them, and the capabilities to succeed," he said, adding that NATO allies "must be better equipped to help stop the spread of the world's most dangerous weapons."
"We will continue to develop missile defence to counter a growing Iranian capability, provided the technology is proven and it is cost effective," he told a top-level security conference in Munich, southern Germany.
"We will do so in consultation with you, our NATO allies, and with Russia," he said.
His remarks suggested that Washington could review the multi-billion dollar project.
Late last month, a senior US official told AFP that he expected President Barack Obama to order a review to see how the system is evolving and whether it is cost effective.
"I would not at all be surprised for a new administration to want to review: Where do we stand in this programme now? What's the level of technological development? What are the costs?" the official said.
The United States has been negotiating with Poland and the Czech Republic to install 10 missile interceptors, which would not carry explosive warheads, 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 that the shield is only directed at "rogue states", primarily Iran.
Russia had threatened to deploy Iskander missiles to Kaliningrad, a Russian exclave wedged between NATO and EU members Poland and Lithuania, if Washington did not halt the planned defence extensions.
But Moscow has lately softened its tone, apparently reassured by Washington's stance.