MOSCOW -- Russian lawmakers on Tuesday voted unanimously to formally pull out of a key Cold War-era security deal, more than eight years after Moscow halted its participation.

The vote came less than a week after President Vladimir Putin introduced a draft bill on May 10 "denouncing" the Treaty of Conventional Armed Forces in Europe, which aimed to prevent Cold War rivals from massing forces at or near mutual borders. The deal was signed in November 1990, but not fully ratified until two years later.

Russia first announced its intention to completely withdraw from the treaty in early 2015. Since last February, Moscow's military operation in Ukraine has seen hundreds of thousands of Russian troops pour into the country, which shares a border with NATO members Poland, Slovakia, Romania and Hungary.

On Tuesday, Putin's designated envoy told the State Duma that NATO countries had "made it impossible" for Russia to remain in the treaty by allowing for the alliance's expansion into Central and Eastern Europe.

Deputy Foreign Minister Sergey Ryabkov also described the treaty as "contrary to Russia's security interests" in an interview published Monday in Parliamentskaya Gazeta, a weekly published by the State Duma.

Ryabkov's remarks were echoed by key deputies during the parliamentary session Tuesday. State Duma speaker Leonid Slutsky charged that the treaty had "long existed only on paper," while Andrey Kartapolov, the chairman of Russia's parliamentary committee, said that it had been rendered obsolete by NATO's placing of military infrastructure in Central and Eastern European member states.

Ryabkov told lawmakers that completing the withdrawal process would take about six months.