BUSHEHR, Iran, (AFP) - Iran began testing its first nuclear power plant on Wednesday in the face of deep international concern over its atomic drive and said the long-delayed project could go on line within months, defying international calls that it halt the sensitive nuclear process. Officials from Iran and Russia, which has been involving in building the power station for the past 14 years, watched over the start of the pre-commissioning in the Gulf port of Bushehr. "As for a timetable, the tests should take between four and six, seven months," the head of Iran's Atomic Energy Organisation Gholam Reza Aghazdeh said at a press conference in Bushehr. "And if they go smoothly, then it (the launch of Bushehr) will be even sooner." He also said Iran is now operating 6,000 centrifuges to enrich uranium, defying international calls that it halt the sensitive nuclear process which is at the heart of Western fears it is secretly trying to build the atomic bomb. "We have 6,000 centrifuges working and we plan to increase them. In the next five years we plan to have 50,000 centrifuges," Aghazdeh told reporters. Iran has rejected repeated calls by the UN Security Council - of which Russia is a permanent member - for a halt to enrichment, despite three sets of sanctions being imposed for its defiance. The UN nuclear watchdog had said in a report last week that Iran was slowing the expansion of its enrichment activities, with 3,964 centrifuges actively operating in Natanz. The visiting head of the Russian nuclear agency, Sergei Kiriyenko, announced that construction of the 1,000-megawatt Bushehr plant had been completed but that Russia would remain involved for one year after it goes on stream. "We have reached a deal to establish a joint venture to operate the plant," he said, adding that the two sides were also in talks to sign a 10-year contract for the delivery of nuclear fuel by Russia. Israeli Defence Minister Ehud Barak called for tougher sanctions against Iran. "Although the plant is not a central part of Iran's military nuclear operations, the announcement of completion of work shows the importance of the concrete steps that the free world, led by the United States, should take as time is pressing," Barak said. As part of the pre-launch process, Iran was carrying out comprehensive tests of equipment at the plant which Kiriyenko said involved loading dummy fuel rods into the reactor. "Most of the systems have had more than 97pc of the equipment installed," Kiriyenko said, adding that some parts that required further testing included heat insulators. Bushehr was first launched by the US-backed shah in the 1970s using German contractors but was shelved after the Islamic revolution until Russia became involved in 1995. The International Atomic Energy Agency, which has been investigating Iran's nuclear programme for six years, said last week it had been informed by Tehran that the loading of fuel into the reactor was scheduled to take place during the second quarter of 2009.