U.S. and Russian officials have failed to narrow differences in their latest round of talks, but both sides have expressed readiness to continue discussions.

Acting Under Secretary of State for Arms Control John Rood told the Reuters news agency by telephone substantial differences remain after Monday's talks in Moscow. But he cited improved understanding of the concerns of both sides and their potential solutions as an indication of progress.

Earlier, Russia's Deputy Foreign Minister, Sergei Ryabkov, said the two countries did not manage to bring their approaches on arms control issues closer together, but he said Moscow is satisfied with the talks.

The agenda included U.S. plans for a missile defense shield in central Europe and a nuclear arms reduction agreement that expires next year.

In his comments, Ryabkov expressed optimism over chances for an agreement on replacing the 1991 Strategic Arms Reduction Treaty (START), set to expire in December 2009.

Russia has strongly opposed the U.S. missile defense plans as a threat to its security.

U.S. officials say the proposal to place 10 interceptor missiles in Poland and guidance radar in the Czech Republic is aimed at protecting European allies against threats from countries such as Iran.

Some information for this report was provided by Reuters.