The Russian Defense Ministry late Thursday denied the U.S.'s claim that four Syria-bound missiles crashed in Iran.

Earlier on the same day a U.S. official had claimed that four Russian cruise missiles aimed at targets in Syria instead crashed in Iran, declining to comment on whether there were any casualties.

The official, who spoke on the condition of anonymity, said the missiles landed in Iran on Wednesday, but did not provide details about where they might have landed. The official was confirming a story first reported by CNN.

Meanwhile, Iran, Russia's partner in backing Syrian President Bashar Assad, despite denying having any military forces in Syria, has reportedly lost a senior general of the Revolutionary Guards to opposition forces.

General Hossein Hamedani was killed near Aleppo where he was advising the Syrian army on their battle against Islamic State of Iraq and al-Sham (ISIS), the organization said in a statement on Friday, despite Iran denying any participation in military action in the country.

The general was killed late Wednesday, the statement said. Iran is Assad's main regional ally and has provided military and economic support during Syria's four-year-old civil war.

Hamedani was a veteran of the 1980 to 1988 Iran-Iraq war and was made deputy chief commander of the elite forces in 2005.

In the biggest deployment of Iranian forces yet, sources told Reuters last week that hundreds of troops had arrived since late September to take part in a major ground offensive planned in western and northwestern Syria.