Russia's State Duma, or lower house of parliament, might block a new strategic arms treaty (START) with the United States, if it is not linked with missile defense, the Duma's speaker said Tuesday.

"We will not ratify it, if it does not take into account the link between strategic offensive weapons and missile defense," Boris Gryzlov was quoted as saying by the Interfax news agency.

Gryzlov told his Bulgarian counterpart, Tsetska Tsacheva, Tuesday U.S. plans to deploy elements of a missile defense shield in eastern Europe was "a particularly sensitive issue for Russia."

He also asked her whether Bulgaria would join the planned deployment.

Tsacheva replied the project "has not been discussed either in the government, or in parliament," adding "what is meant here is only NATO's ideas, voiced by U.S. officials through the mass media."

Russia and the United States have been working on a new arms control deal since Russian president Dmitry Medvedev and U.S. president Barack Obama met in April last year, but they failed to reach a pact before START-1 expired in December.

The U.S. missile defence plans have become a major sticking point in the nuclear disarmament negotiations.

On Feb. 12, the U.S. ambassador to Bulgaria James B. Warlick said there had been informal discussions at different levels "in Sofia and in Washington" about basing parts of the American missile shield in Bulgaria.

Bulgarian Prime Minister Boyko Borisov also said he supported plans for taking part in a new U.S. missile defense system in Europe.

However, Bulgaria informed Russia on Feb. 19 there were no official negotiations with the U.S. about the planned missile defense system.

Russian Foreign Minister Sergei Lavrov reiterated on March 9 the new arms control deal would link strategic offensive and defensive weapons, which was agreed by Medvedev and Obama during their meeting last April.

U.S. Secretary of State Hillary Clinton is to meet Lavrov in Moscow on March 18-19, when both sides are expected to discuss the START treaty.

The Kremlin said on Saturday that, during a telephone conversation, Medvedev and Obama agreed it was now possible to talk about specific dates for signing the new treaty.

The Russian daily, Kommersant, meanwhile reported newly elected Ukrainian President Viktor Yanukovych suggested Kiev as the venue for the signing when he met Medvedev in Moscow on March 5 and Moscow had shown interest.

Anna German, deputy head of the Ukrainian presidential administration, said Kiev's bid to host the signing ceremony was part of Yanukovych's efforts to serve as "the bridge between the East and the West."