Iran warned Sunday it may limit cooperation with the UN nuclear watchdog, expressing disappointment over the agency's recent report that was critical of Teheran. The International Atomic Energy Agency, in a report to the UN Security Council last week, suggested Iran was stonewalling investigators and possibly withholding information crucial to determining whether it conducted research on nuclear weapons. Iranian Foreign Ministry spokesman Mohammad Ali Hosseini said Sunday the IAEA "could present a better report," adding Iran may have to set "new limits" on its cooperation with the agency. Iran's newly elected parliament speaker Ali Larijani made a similar threat on Wednesday. Parliament on Sunday elected Larijani, formerly the country's top nuclear negotiator, to the powerful post of speaker for a year. The choice of Larijani for the influential job boosts his standing ahead of 2009 elections in which he is expected to challenge President Mahmoud Ahmadinejad for the presidency. There is growing opposition to Ahmadinejad from other conservatives such as Larijani and clerical leaders, partly over his confrontational approach in the nuclear standoff with the West. Iran is under growing pressure from the IAEA to explain what could be secret nuclear weapons work and it has become increasingly defensive on the issue. Iran insists its nuclear program is for peaceful purposes. Iran is resisting a strong IAEA push for answers to allegations it tried to make nuclear arms. It refuses to compromise on the key demand that it stop uranium enrichment. For years, Iran has shrugged off offers of economic and political rewards in exchange for an enrichment freeze. It has thumbed its nose both at UN Security Council demands that it do so, even after sanctions were imposed, and at veiled US threats of a military action. Instead, it exploited international indecision and expanded and improved its enrichment capability. Diplomats said the tone of the IAEA report was unusually tough and reflected deep frustration at Iran's lack of cooperation. Briefing IAEA board members three days after the report's release, Olli Heinonen - the IAEA's deputy director general in charge of the agency's Iran file - said Iran's possession of nuclear warhead diagrams was "alarming." Iran remains defiant. In a statement from its UN Mission last week, Teheran again rejected allegations of an undeclared weapons program as "baseless," "totally false," and aimed at undermining the country's cooperation with the IAEA. Asked Friday whether the IAEA's new assertiveness was due to US lobbying of the agency, Iranian Foreign Minister Manouchehr Mottaki told the AP that Washington tries "to use any possible capacity as potentiality for their political purposes." Fears that Iran might want to make the bomb are as old as the discovery five years ago that it had assembled the nuts and bolts of a uranium enrichment program. Enrichment can turn uranium into the fissile material used in nuclear warheads. But it can also be used to generate power and is allowed under the Nuclear Nonproliferation Treaty. Iran insists it has a right to enrich uranium. Starting last year, the IAEA began focusing on probing for evidence of activities that point more directly to a possible clandestine weapons program. Based on its own information and intelligence from the US and other board members, it has asked - in vain - for substantive explanations for what seem to be draft plans to refit missiles with nuclear warheads; explosives tests that could be used for a nuclear detonation; military and civilian nuclear links and a drawing showing how to mold uranium metal into the shape of warheads.