Russian President Vladimir Putin said on Thursday that a U.S. military attack on Iran would be a catastrophe for the Middle East that would trigger a surge in violence and a possible refugee exodus.
He added that it would trigger an escalation of hostilities with unpredictable results.
Putin, speaking during his annual televised question and answer session, said Moscow believed Tehran was in full compliance with its nuclear commitments and called sanctions against Iran groundless.
Iran on Thursday shot down a U.S. military drone it said was on a spy mission over its territory but Washington said the aircraft was targeted in international air space in "an unprovoked attack".
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The incident fanned fears of wider military conflict in the Middle East as U.S. President Donald Trump pursues a campaign of to isolate Iran over its nuclear and ballistic missile programmes and role in regional wars.
It was the latest in an escalating series of incidents in the Gulf region, a critical artery for global oil supplies, since mid-May including explosive strikes on six oil tankers as Tehran and Washington have slid towards confrontation.
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Iran has denied involvement in any of the attacks, but global jitters about a new Middle East conflagration disrupting oil exports have triggered a jump in crude prices. They surged by more than $3 to above $63 a barrel on Thursday.
Tensions flared with the U.S. pullout last year from world powers' 2015 nuclear accord with Iran and have worsened as Washington imposed fresh sanctions to throttle Tehran's vital oil trade and Iran retaliated earlier this week with a threat to breach limits on its nuclear activities imposed by the deal.
Upping the ante, Washington said on Monday it would deploy about 1,000 more troops, along with Patriot missiles and manned and unmanned surveillance aircraft, to the Middle East on top of a 1,500-troop increase announced after the May tanker attacks.