Russia thinks the launch of an Iranian rocket into space raises suspicion over the true aim of its nuclear programme, a foreign ministry official has said.
Iran launched the rocket with a big televised fanfare on Monday
"Long-range missiles are one of the components of a [nuclear] weapons system," Deputy Foreign Minister Alexander Losyukov told Interfax.
Therefore Monday's test launch of Iran's Explorer-1 space rocket was "of course, a cause for concern", he said.
Iran insists its nuclear programme is purely for peaceful energy production.
Correspondents say the statement by Mr Losyukov appeared to indicate that Moscow increasingly shares Western concerns about Tehran's nuclear course.
"It increases suspicion of Iran regarding its possible desire to create a nuclear weapon," he was quoted as saying.
Iran said the rocket which was test-fired would be used to launch research satellites.
The US State Department said the launch was "troubling", as it was an example of the same technology behind long-range ballistic missiles.
In the past, Russia has been more sceptical than some Western powers about Iran's missile capability, saying it would take a long time to build long-range missiles.