US Defence Secretary Robert Gates has rejected the claim that a decision to shelve a plan for missile defence in Europe was a concession to Russia.
Writing in the New York Times, Mr Gates said Russia's attitude "played no part" in his recommendation to President Barack Obama to drop the plan.
Mr Gates said the aim was to deal with potential threats from Iran.
A new system will be able to provide such a defence sooner and more effectively, he said.
Under the original plan, the US signed a deal in August 2008 with Poland to site 10 interceptors at a base near the Baltic Sea, and with the Czech Republic to build a radar station on its territory.
Russia, which had always seen that plan as a threat, welcomed the decision to abandon it.
However, there has been criticism of the decision in conservative circles in the US.
'Greater flexibility'
Mr Gates, a Republican who also served as defence secretary during George W Bush's final years as president, described initially recommending the missile defence plan in late 2006.
"At the time, it was the best plan based on the technology and threat assessment available," he said.read more
