* West suspects clean-up of nuclear traces at military site
* IAEA may return empty-handed from any visit - diplomats
* Tehran says Parchin is a conventional military complex
The U.N. nuclear watchdog acknowledged on Wednesday it might not find anything if allowed access to an Iranian military facility, in an apparent reference to suspected clean-up work there, diplomats said.
Herman Nackaerts, deputy director general of the International Atomic Energy Agency (IAEA), made the comment during a closed-door briefing where he showed satellite imagery indicating Iran had now partly paved the site, they said.
The picture was the latest sign of what Western officials suspect is an Iranian attempt since early last year to remove or hide any evidence of illicit nuclear-related activity at Parchin, located southeast of the capital Tehran.
In response to a question, "he (Nackaerts) said there is a chance they won't find anything", in view of the suspected sanitisation efforts, said one diplomat who was at the meeting.
Nackaerts made no public comment.
The U.N. agency believes Iran may have carried out explosives tests relevant for nuclear weapons development at Parchin, possibly a decade ago, and has been pressing Tehran for more than a year to be allowed visit the sprawling facility.
Iran, which denies Western allegations that it seeking the capability to make nuclear weapons, says Parchin is a conventional military complex and rejects accusations that it is trying to remove any evidence.
The IAEA said in a report to member states last week that Iran had asphalted a "significant proportion" of the specific part of Parchin it wants to inspect.
It did not say why Iran may have decided to do this, but one Western official who attended Wednesday's briefing said it could be a bid to cover up any remaining traces there.
Iran's ambassador to the IAEA, Ali Asghar Soltanieh, declined to speak to reporters when he left the meeting room.
The U.N. agency wants to check Parchin as part of its long-stalled investigation into suspected atomic bomb research by Iran, which says its nuclear programme is entirely peaceful.
Iran says it first needs to agree with the IAEA on how the broader inquiry is to be conducted before granting access.
Citing satellite imagery, Western diplomats earlier this year said that Iran appeared to be rebuilding the site, after previously razing smaller buildings and removing soil.
Experts say that while it may now be difficult to find any evidence, it could still be possible to locate any traces of nuclear materials with the IAEA's sophisticated equipment.
"The more they (Iran) do, the less likelihood there is of picking up something easily," one Western envoy said.
"(But) I think the chances of wiping out every trace of whatever might have been going on there is very slim."