By Steve Gutterman
MOSCOW (Reuters) - The Russian parliament on Wednesday urged the United States not to strike Syria, warning that military action could be a "crime against the Syrian people" but stopping short of threatening countermeasures.
Air strikes would "lead to new civilian deaths, further destruction of vital infrastructure and, in the end, an irreversible humanitarian catastrophe," the State Duma, the lower chamber, said in a declaration adopted by unanimous vote.
The non-binding declaration by the Duma, dominated by the Kremlin-controlled United Russia party, echoed the vociferous opposition to U.S. military action of President Vladimir Putin and his government.
"Those who are prepared to give an order for such an attack should understand that such actions could be qualified as a very crude violation of international law and as a crime against the Syrian people," it said.
It warned that a strike could "place nuclear and chemical security in the region under threat", a reference to Syria's chemical weapons stocks and a small reactor that contains radioactive uranium.
Russia has been Syrian President Bashar al-Assad's most powerful backer during the civil conflict that has killed more than 100,000 people since 2011, delivering arms and - with China - blocking three U.N. resolutions meant to pressure Assad.
The Duma expressed support for Russia's proposal to place Syria's chemical arsenal under international control, which Putin said on Tuesday would only succeed if the United States and its allies abandoned plans for possible military action.
The vote followed debate in which lawmakers proposed Russia consider taking action to punish the United States if it does strike - such as withdrawing from the New START nuclear arms control pact, increasing weapons sales to Syrian ally Iran or curtailing cooperation with the United States on Afghanistan.
No such measures ended up in the declaration, but lawmakers said they could be included in a second statement that could be put to a vote if the United States strikes Syria.
The Duma criticized the U.S. Congress for allegedly refusing to see Russian lawmakers who offered to travel to Washington for talks on Syria, saying it "could place interaction on key issues on the Russian-American agenda in question".
(Editing by Andrew Roche)