"We welcome the approval of the treaty by the US Senate," Lavrov was quoted as saying by the Interfax news agency.
Lavrov added however that the text of the resolution had been "somehow amended compared to the initial draft."
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"The ministry and the parliament, we need some time to study the documents of the US ratification," he said.
START restricts the former Cold War foes to a maximum of 1,550 deployed warheads each, a cut of about 30 percent from a limit set in 2002, and 800 launchers and bombers.
