"Substantive progress has been made, but it was not formalized in documentary form," Ryabkov said, commenting on Thursday's meeting between Russian President Dmitry Medvedev and his U.S. counterpart Barack Obama on the sidelines of the G8 summit in Deauville, France.

Moscow has been concerned by a U.S. reluctance to provide guarantees that its European missile defense system will not be directed against Russia.

"We are ready for missile defense cooperation, we are ready to create joint systems, but we have yet to see whether our partners are ready for that," Ryabkov said.

"We cannot base our security on promises."

Medvedev warned last Wednesday that Russia would have to build up its nuclear capability if NATO and the United States failed to reach an agreement with Moscow on European missile defense cooperation.

Moscow has warned it might pull out of the new START Treaty.

Russia and NATO agreed to cooperate on the so-called European missile shield during the NATO-Russia Council summit in Lisbon in November 2010. NATO insists there should be two independent systems that exchange information, while Russia favors a joint system.

Russia is opposed to the planned deployment of U.S. missile defense systems near its borders, claiming they would be a security threat. NATO and the United States insist that the shield would defend NATO members against missiles from North Korea and Iran and would not be directed at Russia.