Israel has condemned as unacceptably slow Iran's cooperation with a U.N. watchdog inquiry into suspected nuclear bomb research and accused Tehran of providing "false" explanations for its disputed activities.
Iran, which says its nuclear program is peaceful and that it is Israel's assumed atomic arsenal that threatens Middle East peace, insisted there had been "steady and constant progress" in its cooperation with the International Atomic Energy Agency.
The contrasting statements by the two arch-enemies were made during a board meeting this week of the U.N. agency, where IAEA chief Yukiya Amano said Iran had finally begun to engage with an investigation into allegations that it has worked on designing a nuclear warhead, but that more was needed.
Western envoys cautiously welcomed Iran's increased nuclear transparency, while also calling for Tehran to pick up the pace of its cooperation. But Israel's ambassador suggested Iran was just trying to buy time while pressing on with its nuclear work.
Widely believed to be the Middle East's only nuclear-armed power, Israel sees Iran's atomic program as a direct threat and has in the past warned it could carry out unilateral strikes on Iranian nuclear sites. Iran rejects accusations that it has been trying to develop a nuclear bomb capability.
"Iran continues to abuse what is termed as a 'step-by-step' approach to the resolution of outstanding issues," Israeli Ambassador Merav Zafary-Odiz said, referring to a phased cooperation pact agreed in November between Iran and the IAEA.
"This pace of investigation is unacceptable ... Iran will continue to provide false explanations and to hide the true nature of its activities," she said, without giving details.
Because of a Jewish holiday, Zafary-Odiz did not deliver her statement during Wednesday's IAEA board debate on Iran, but it was posted later on the United Nations agency's web site.
Israel is also deeply skeptical of U.S.-led efforts to reach a final international accord to scale back a nuclear program which Iran says is for energy purposes but the West fears may be a covert bid to develop the means and expertise to build bombs.
U.S. officials say it is vital for Iran to resolve the IAEA's concerns if the parallel negotiations between Tehran and the United States, France, Germany, Britain, China and Russia on the long-term agreement to settle the dispute are to succeed.
Those talks aim to set verifiable, civilian limits to Iran's nuclear program and end punitive sanctions imposed on Tehran.
Israeli Prime Minister Benjamin Netanyahu has complained that sanctions on Iran are being eased prematurely.
Seeking to narrow big differences between Iran and the powers on what such a deal should look like, their experts were meeting in Vienna this week ahead of the next round of political level talks on June 16-20, also in the Austrian capital.
The sides aim to hammer out an agreement by a self-imposed July 20 deadline, although some diplomats and analysts say the talks will likely have to be extended.
The IAEA's inquiry focuses specifically on what it calls the possible military dimensions of Iran's atomic activities.
Iran says the accusations are baseless but has offered to address them since pragmatist Hassan Rouhani took office as Iranian president last year, partly on a platform to end the Islamic state's international isolation.
"We do not recognize the ... unsubstantiated allegations," Iran's ambassador to the IAEA, Reza Najafi, told the board in a statement made available to Reuters on Thursday. "However, we have already announced our readiness to cooperate with the IAEA on some of the ambiguities in order to clarify them."
Last month, Iran gave the IAEA information requested in the inquiry as to its purpose in developing Exploding Bridge Wire (EBW) detonators, which can be used to set off an atomic explosive device. Iran says it was for civilian use.
In a meeting in Tehran on May 20, Iran also agreed to address two other areas of the investigation by Aug. 25.
Western governments regard Iran's increased readiness to cooperate as positive but are likely to remain skeptical until it has cleared up all allegations of illicit atomic work.
Editing by Mark Heinrich