The United States is ready to provide Moscow with written assurance that the NATO-backed Euro missile defense shield is not directed against Russia, a U.S. under secretary of state said on Tuesday. \"The missile defense system we are establishing in Europe is not directed against Russia. We have said that publicly and privately, at many levels,\" U.S. Under Secretary of State for Arms Control and International Security Ellen Tauscher said. \"We are prepared to put it in writing.\" But Tauscher said Washington could neither provide a legally binding commitment nor \"agree to limitations on missile defenses, which must necessarily keep pace with the evolution of the threat.\" She also said that the mission of missile defense in Europe is \"to counter launches from the Middle East, which would be few in number and at an early stage of technology.\" The U.S. official also said Russia and the United States may not reach specific agreements on the European missile shield by the NATO summit in Chicago due in May. Tauscher said she did not expect breakthroughs during the forthcoming summit, adding that the event\'s principal result could be to stress once again the role of NATO during a period of economic uncertainty. In an attempt to persuade Moscow that the missile defense system in Europe poses no threat, a Pentagon official invited Russia to use its own radars and other missile defense elements to track down U.S. missile-defense flight tests, Reuters reported. Army Lieutenant General Patrick O\'Reilly, director of the Pentagon\'s Missile Defense Agency, told the Atlantic Council forum that planned Standard Missile-3 interceptors would be ineffective as anti-missile interceptors against Russia, whose strategic deterrent missiles are launched from deep inside its territory. \"These are smaller missiles,\" O\'Reilly said, adding that they \"can\'t reach that far.\" Russia and NATO agreed to cooperate on the so-called European missile defense system at the Lisbon summit in November 2010. NATO insists there should be two independent systems that exchange information, while Russia favors a joint system with full-scale interoperability.