Russia used Iran as a base from which to launch air strikes against Syrian militants for the first time, widening its air campaign in Syria and deepening its involvement in the Middle East.
In a move underscoring Moscow's increasingly close ties with Tehran, long-range Russian Tupolev-22M3 bombers and Sukhoi-34 fighter bombers used Iran's Hamadan air base to strike a range of targets in Syria on Tuesday.
It was the first time Russia has used the territory of another nation, apart from Syria itself, to launch such strikes since the Kremlin launched a bombing campaign to support Syrian President Bashar al-Assad in September last year.
It was also thought to be the first time that Iran has allowed a foreign power to use its territory for military operations since the 1979 Islamic revolution.
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The Iranian deployment will boost Russia's image as a central player in the Middle East and allow the Russian air force to cut flight times and increase bombing payloads.
The head of Iran's National Security Council was quoted by state news agency IRNA as saying Tehran and Moscow were now sharing facilities to fight against terrorism, calling their cooperation strategic.
Both countries back Assad, and Russia, after a delay, has supplied Iran with its S-300 missile air defence system, evidence of a growing partnership between the pair that has helped turn the tide in Syria's civil war and is testing US influence in the Middle East.
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Relations between Tehran and Moscow have grown warmer since Iran reached agreement last year with global powers to curb its nuclear program in return for the lifting of UN, EU and US financial sanctions.
President Vladimir Putin visited in November and the two countries regularly discuss military planning for Syria, where Iran has provided ground forces that work with local allies while Russia provides air power.
Iraqi Prime Minister Haider al-Abadi said on Tuesday Iraq, which lies between Iran and Syria, had granted Russia permission to use its air space, on the condition the planes use corridors along Iraq's borders and not fly over Iraqi cities.
Abadi said the same permission has been given to air forces of a separate US-led coalition against Islamic State flying to Syria from Kuwait.
Russia also gave advanced notice to the US-led coalition battling Islamic State in Syria and Iraq, complying with the terms of a safety agreement meant to avoid an accidental clash in the skies, the US military said.
The ministry said Tuesday's strikes had targeted Islamic State as well as militants previously known as the Nusra Front in the Aleppo, Idlib and Deir al Zour provinces.
"As a result of the strikes five large arms depots were destroyed ... a militant training camp ... three command and control points ... and a significant number of militants," the ministry said in a statement.
The destroyed facilities had all been used to support militants in the Aleppo area, it said, where battle for control of the divided city, which had some 2 million people before the war, has intensified in recent weeks.
The Syrian Observatory for Human Rights, a UK-based war monitor, said heavy air strikes on Tuesday had hit many targets in and around Aleppo and elsewhere in Syria, killing dozens.