Russia cannot be allowed to veto NATO membership for former Soviet states such as Ukraine and Georgia, US Secretary of State Condoleezza Rice said in an interview published on Sunday.
Rice said Moscow should not be permitted to profit from its military victory over Georgia last month, and said its 15-year effort to join the World Trade Organisation (WTO) was in danger.
"We will not permit Russia to veto the future of NATO, neither the countries offered membership nor their decision to accept it," Rice said in an opinion piece published in Greek in the Typos newspaper.
"We and our European allies will give our help to Georgia ... The United States and Europe strongly support the independence and the territorial integrity of Russia's neighbours," she said.
At an April summit, NATO stopped short of putting Ukraine and Georgia immediately on the path to joining the transatlantic military alliance, but pledged that the two ex-Soviet states would one day become members.
While the United States has backed the entry bids of both Georgia and Ukraine, allies including Germany, France and smaller NATO states have opposed them for fear of provoking Russia. Russia regards both countries as part of its traditional sphere of influence in which it has "privileged interests".
In Ukraine itself, where the east of the country is broadly pro-Russia, the idea of joining NATO is unpopular with the majority of the population, according to opinion polls.
Rice reiterated U.S. warnings that Russia's military action in Georgia could derail its efforts to join the WTO and the Organisation for Economic Cooperation and Development (OECD), a grouping of democratic market economies.
EU Trade Commissioner Peter Mandelson has argued it would be counter-productive to withhold WTO membership to punish Moscow.
U.S.-ally Georgia tried to retake control of its pro-Russian South Ossetia province in early August but its troops were quickly defeated by Russia. Moscow's troops drove deep into Georgian territory, drawing international condemnation, before pulling back.
Russia, which on Friday announced plans to bolster its nuclear deterrent, has until Oct. 10 to comply with a French-brokered deal to withdraw its troops from security zones around Georgia's breakaway zones of South Ossetia and Abkhazia.