"We will not ratify it if the questions of the link between strategic offensive weapons and missile defence are not examined," Duma speaker Boris Gryzlov said at a meeting with his Bulgarian counterpart.

Gryzlov said that moves by the United States to install missile defence facilities in countries such as Bulgaria are of a "particularly sensitive character for Russia."

Some observers have said that a Russian insistence on a link with missile defence is the main problem holding up agreement on a successor to the 1991 Strategic Arms Reduction Treaty (START) between the two countries.

Gryzlov is a top official from the ruling United Russia party of Prime Minister Vladimir Putin and is known for rarely stepping away from the official line.

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