Acrimony marked the opening day of the International Atomic Energy Agency's (IAEA) 151-nation annual conference in Vienna, the Associated Press reported Monday.
The conflict centered on a rhetorical tennis match between Washington and Tehran over the Islamic Republic’s nuclear activities and refusal to cooperate with IAEA inspectors.
Nine years after the United Nation's learned Tehran was running a clandestine uranium enrichment facility behind the nuclear watchdog's back the issue remains fore and center in Vienna. To date the UN has imposed four sets of sanctions on Iran for its refusal to stop its enrichment program and fully cooperate with IAEA inspection efforts.
Tehran insists its nuclear program only has civilian aspirations, but Western diplomats maintain they have intelligence suggesting the Islamic Republic is actively pursuing the development of an atomic bomb.
Officials from Washington warned other nations at the conference that Tehran's moving its uranium enrichment facilities underground was a material step towards being producing the fissile core for a nuclear warhead - and described Iran's nuclear program as being a product of "denial, deceit and evasion."
"Iran has continued to engage in a long-standing pattern of denial, deceit, and evasion, in violation of its nonproliferation obligations," US Energy Secretary Steven Chu told the assembled delegates.
"Time and time again, Iran has refused to satisfy legitimate concerns about the nature of its nuclear program — selectively rejecting IAEA requests for access to, and information about, its nuclear facilities," Chu added.
Tehran, however, said Western pressure was to blame for its decision to relocate thousands of centrifuges to hardened underground facilities and for refusing to open its nuclear activities to IAEA inspectors.
"Hostile positions and measures of (a) few countries," Iranian Vice President Fereydoun Abbassi Davani responded, "force other nations to make their peaceful activities ... secret and put them underground."
Iran' recently announced that it would increase production of uranium enriched to a higher level than normally needed for reactor fuel and do so at a hardened underground facility near the central of Qom.
Chu answered Davani's purported fears, saying, "expanding, and moving underground, its enrichment to this level marks a significant provocation and brings Iran still closer to having the capability to produce weapons grade uranium.
"Pursuing this course raises serious questions over Iran's peaceful intent," he said.
Tehran is expected to attempt to deflect attention from its own nuclear program during the IAEA session by trying to shift the spotlight on Israel's nuclear plant at Dimona and activities there.
Iran, and Arab nations, have said they want to raise Jerusalem's purported nuclear capabilities for discussion at the nuclear watchdog.
Israel, however, is not a signatory to the Nuclear Non-Proliferation Treaty (NPT) like Tehran and the nuclear watchdog has no purview over its nuclear activities. As a result, raising Israel's nuclear program is a non-sequitur with little potential to lead anywhere.
Jerusalem maintains a policy of "nuclear ambiguity," refusing to discuss whether it possesses nuclear weapons. On Friday, Israel became an associate member of the prestigious European Organization for Nuclear Research (CERN).