Pentagon officials are declining comment on reports that Russia has tested a new missile apparently designed to defeat U.S. missile defenses.
The Washington Times newspaper says the Russian test involved a long-range missile with a new kind of jet-powered last stage.
U.S. sources confirm a Russian missile test about two weeks ago. But Pentagon officials decline, as a matter of policy, to discuss what are considered intelligence matters.
According to the Washington Times, the mobile SS-25 missile included a last stage built like a cruise missile - one capable of flying and maneuvering at high speed in the Earth's atmosphere.
The Times says such a system could be intended to circumvent planned U.S. missile defenses.
The Bush administration has said repeatedly its desire for missile defenses is not aimed against Russia but instead against possible attacks from rogue states like North Korea and Iraq.
U.S. and Russian officials have begun intensive discussions on missile defense issues, including modification of the 1972 Anti-Ballistic Missile Treaty that could interfere with U-S testing and deployment plans.
U.S. officials are trying to develop a variety of anti-missile systems, including airborne and sea-borne weapons along with a ground-based interceptor.