BERLIN, March 31: Britain, France and Germany criticized Iran on Wednesday for starting up a uranium conversion plant and demanded Tehran explain itself.

The United States says Iran's nuclear programme is a front to build an atomic bomb, while the three European governments defied Washington in September by offering to share technology with Tehran if it stopped its nuclear fuel enrichment programme.

The statement by the EU "Big Three" marks their growing frustration with Iran. The German foreign ministry said it had noted Iran's announcement last week to start up the uranium conversion plant near its central city of Isfahan.

"This announcement sends the wrong signal regarding Iran's readiness to implement a suspension of its activities relating to uranium enrichment," the ministry said in a statement.

"It will make it more difficult for Iran to restore international confidence in its activities. Iran must explain its announcement and its intentions." Iran's explanation would be of the utmost importance, the ministry said, adding that the foreign ministries of France and Britain had issued the same statement.

Iran pledged to suspend activities related to uranium enrichment in October as a goodwill gesture while under intense US pressure to prove it was not seeking nuclear weapons.

In February it promised to suspend all "remaining enrichment activities" after sparking a row by interpreting the suspension in the narrowest possible sense.

Uranium conversion plants are key to the enrichment process. They convert uranium oxide concentrate into uranium hexafluoride gas, which is placed in centrifuges, the machines that enrich uranium. The element can then be used to make fuel or weapons.

The Vienna-based International Atomic Energy Agency (IAEA) said on Saturday there was nothing controversial about opening the plant. Tehran insist its nuclear programme is solely for the peaceful generation of electricity.

But an internal IAEA report said some inspections in Iran had been "managed" by the Iranians, who refused to let inspectors take pictures with UN cameras or use their own electronic devices.

A group of Western diplomats who follow the IAEA said recent intelligence had provoked suspicion that Tehran had not stopped enriching uranium but moved enrichment activities away to a plant discovered at Natanz to smaller sites that are part of a parallel programme UN inspectors have not uncovered.

"We've got lot of intelligence about small enrichment plants for some months," one Western diplomat said. Iran's ambassador to the United Nations in Vienna, Pirooz Hosseini, said the charges that smaller plants were continuing enrichment were "baseless" and "an attempt to destroy the fruitful cooperation between the IAEA and Iran". -Reuters