VIENNA: The United States warned Iran on Wednesday that it faces further international isolation if it fails to address U.N. nuclear watchdog concerns about its atomic activities.

The European Union also used a board meeting of the U.N.'s International Atomic Energy Agency to pile pressure on Iran to stop obstructing an IAEA investigation into suspected atom bomb research by Tehran, which denies the charge.

Washington and its Western allies were signalling their determination that Iran must give the IAEA access to sites and documents, regardless of broader talks between Tehran and world powers that resumed last week.

Some diplomats say Iran is using its meetings with the IAEA merely for leverage in those negotiations with world powers which, unlike the IAEA, have the power to ease sanctions that they have recently tightened on the major oil producer.

U.S. envoy Joseph Macmanus accused Iran of "provocative actions", particularly its installation of advanced centrifuges that would enable it to speed up its uranium enrichment work.

"We are deeply concerned with what appears to be Iran's unwavering commitment to deception, defiance, and delay," Macmanus told the IAEA's board of governors, according to a copy of his speech to the closed-door session.

Western countries fear Iran is enriching uranium to develop the capacity to build nuclear weapons and have imposed several rounds of sanctions. Iran says the programme is legitimate and intended for purely peaceful purposes.

Israel says Tehran is secretly trying to develop a nuclear weapon and has threatened pre-emptive strikes if it deems diplomacy ultimately futile.

The Vienna-based IAEA has been trying for more than a year to persuade Iran to give it the access it says it needs for its stalled investigation, so far without progress.

EU SEES IRAN "PROCRASTINATION"

Iran has refused IAEA requests to visit the Parchin military site, where inspectors suspect explosives tests relevant for nuclear weapons development took place, possibly a decade ago.

Iran says it first needs to agree with the IAEA on how the inquiry is to be conducted before allowing any Parchin visit.

The EU told the IAEA board that it "considers ... Iran's procrastination to be unacceptable".

In Almaty, Kazakhstan, last week, six world powers resumed talks with Iran aimed at finding a diplomatic settlement to a decade-old dispute that threatens to trigger a new Middle East war. The only progress was an agreement to hold more talks.

The United States, China, France, Russia, Britain and Germany offered modest relief from economic sanctions in return for Iran scaling back its most sensitive nuclear activity.

Iran called the talks a potential "turning point" but Western officials were more cautious, merely describing the meeting as "useful".

Macmanus said: "I must make clear that we will not accept further delay by Iran in regard to implementing its IAEA obligations and that the separate (big power) diplomatic process cannot be a substitute for such implementation."