Russia is denying reports from unnamed US officials that four of its cruise missiles fired at Syria crashed in Iran.
The missiles were launched from Russian warships in the Caspian Sea on Wednesday as part of an offensive Moscow says is targeting the Islamic State of Iraq and the Levant (ISIL) group and "other terrorists".
The report, citing two US officials, first emerged on CNN. The American network said monitoring by US military and intelligence assets had concluded that at least four missiles crashed as they flew over Iran.
"The US believes, based on intelligence reports of damage assessments, that some buildings were damaged and civilians may have been hurt," the report said.
The Russian defence ministry denied that any of the missiles had fallen short of their targets.
"In contrast to CNN, we do not talk with reference to anonymous sources," the ministry said. "We show the launch of our rockets and the targets they struck."
Spokesman Igor Konashenkov insisted that all the missilies hit their targets.
"Otherwise one would have to admit that the terrorist group ISIL's facilities in Syria ... blew up on their own," he said in a statement.
Russia had displayed graphics of the missiles flying over Iran and Iraq on Wednesday.
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Iranian state media said Iran's defence ministry also rejected the CNN report.
The White House declined to comment on the report from the officials, who asked not to be identified, and the State Department said it could not confirm it.
If confirmed, the crashes would be a blow to the military strength Russia aimed to display in launching what it said were 26 missiles at ISIL targets in Syria about 1,500km from the Caspian Sea on Wednesday.
US officials have already disputed Russian reports that the missiles struck ISIL fighters in Syria.
The US, which leads a coalition bombing ISIL in Syria and Iraq, says Moscow is using ISIL as a pretext to target rebels fighting Syrian President Bashar al-Assad, an ally of Moscow.
"Greater than 90 percent of the strikes that we've seen them take to date have not been against ISIL or al-Qaeda-affiliated terrorists," State Department spokesman John Kirby said on Wednesday.
The Syrian opposition have accused Russia of causing civilian casualties.
Source: Al Jazeera and agencies