Iran stopped inspectors of the International Atomic Energy Agency (IAEA) from conducting design information verification at the country's heavy water reactor at Arak, violating agreements with the United Nations nuclear watchdog.

In a letter to Iran, IAEA chief inspector Olli Heinonen criticised Iran's decision, reminding Iranian authorities that the agreements in question could not be modified unilaterally by Teheran.

Iran said it would only provide design information on Arak or similar sites six months before nuclear material was introduced. The reactor, scheduled to go online in 2009, would have the potential to produce plutonium for nuclear weapons.

In light of to Iran's refusal to cooperate with the IAEA, the EU is considering strengthening its sanctions against Teheran. Israel urged the United States on Thursday to adopt a harder position against Iran, while Iranian Foreign Minister Manouchehr Mottaki reiterated his country's inalienable right to nuclear power.

In the letter dated April 18, the IAEA also confirmed that Iran set up two additional centrifuge cascades for uranium enrichment at is enrichment plant at Natanz, bringing the total number to 8 cascades with a total of around 1,300 centrifuges.

Iran considerably scaled down its cooperation with the nuclear watchdog since the UN Security Council passed sanctions against the country for its refusal to freeze its uranium enrichment programme.

During his visit to Caracas, Mottaki again offered the West 'constructive talks,' but ruled out a stop to Iran's nuclear activities.

'Several (Western) officials have already realized that Iran will not suspend the uranium enrichment process and we therefore hope that they now return to the negotiation table for serious and constructive talks,' he said.

Iran vehemently denies Western accusations that it is pursuing a nuclear weapons capability, maintaining its programme, which it kept secret from IAEA inspectors for 18 years, is solely geared towards energy production.