Iran agreed on Tuesday (July 24) to let inspectors from the United Nation's nuclear watchdog revisit its heavy-water reactor site early next week in a push by the U.N. for more transparency in Iran's disputed nuclear programme. Diplomats said the accord, which came in a second round of negotiations between Iran and the International Atomic Energy Agency (IAEA) to clarify the scope of Iran's atomic activities, was a bid by Tehran to head off more painful U.N. sanctions. Olli Heinonen, the IAEA's deputy director in charge of nuclear safeguards, said Iran agreed to let inspectors return to the Arak heavy-water complex, which is under construction, on Monday or Tuesday -- four months after Iran cut off IAEA access there in protest at existing sanctions. "We have been talking about outstanding issues. This time we agreed on certain fixed time schedule," Heinonen said after meeting Iran's deputy nuclear negotiator Javad Vaeedi at IAEA headquarters in Vienna. "Some events will take place next week, our inspectors will visit the Arak reactor as we agreed last time, and then a week later some inspectors and the team will go (to Iran) to talk about other outstanding issues such as plutonium contamination," he said. Inspectors want to check that Iran is adhering to design data for the reactor given earlier to the IAEA. Diplomats say the risk of Iran using the reactor to process weapons-grade plutonium would rise in the absence of U.N. monitoring. Iran says it is wants to refine uranium only for electricity so it can export more of its oil wealth. But it has been slapped with two sets of sanctions for defying U.N. resolutions demanding it suspend all efforts to produce nuclear fuel. European diplomats said last week Western powers had quietly shelved efforts to toughen penalties against Iran until September to see whether the talks would bring an end to Iranian stonewalling of U.N. inquiries since 2003 and defuse a volatile standoff between Tehran and Western powers. The inspection trip to Arak next week will be a one-off gesture, not a resumption of regular IAEA visits for design verification which Iran has yet to restore, diplomats said. Heinonen said the next step would be to clear up other IAEA questions, such as past Iranian experiments with plutonium and the extent of its uranium enrichment programme. Vaeedi said he would resume talks with Heinonen in Tehran on Aug. 20: "We had a good discussion and constructive progress in this meeting (Tuesday's meeting). Now we are going to move forward in the best mood and with the best effort," he said. Neither man took questions from reporters.