Iran's spiritual leader, Ayatollah Ali Khamenei, on Wednesday said he supported US-Iran talks in Baghdad about improving Iraq's security, state-run television reported. But he warned that the talks would only focus on American responsibilities in Iraq - not Iranian influence in its neighboring country. "The talks will only be about the responsibility of the occupiers in Iraq," the broadcast quoted Khamenei, who has final say on all state matters, as saying. Khamenei rejected that the discussion would involve any talk on Iran-US relations and criticized those who thought that the Islamic country would change its policy toward Washington. "They think that Islamic Republic has changed its firm, logical and defendable policy in rejecting negotiation with the US They are wrong," he was quoted as saying. "How it is possible to negotiate with the arrogant, bullying, expansionist and colonialist government of the US, especially with the current bold, impolite and demanding leaders?" state TV quoted Khamenei as saying. The two countries recently said they would hold ambassador-level talks about Iran's war-torn neighbor, Iraq. Although such talks are seen as a political turnabout, potential for real progress is low as tensions between Iran and the US have continued to escalate. Contacts between the countries have long been taboo, a status enforced by Iran's top leadership - made up of Shi'ite clerics - since the US cut ties with Iran after the 1979 seizure of the US Embassy in Teheran. Khamenei said Iran's Foreign Ministry decided to talk with the US only because Washington did not fulfill its responsibilities in Iraq and accused the US of trying to topple the current Shi'ite-led Iraqi government. "The Iranian Foreign Ministry, based on a request by Iraqi government, decided to remind the US of its responsibilities and duties regarding security ... in a face-to-face negotiation and give them an ultimatum," he was quoted as saying. The broadcast did not elaborate or say what the ultimatum was. The US accuses Iran of secretly trying to develop nuclear weapons and supplying Shi'ite militias in Iraq with roadside bombs used to kill US troops. Iran denies the allegations. During a trip to the region last week, US Vice President Dick Cheney warned that the US and its allies would prevent Iran from acquiring nuclear weapons and dominating the region. Iran has demanded the US leave the Middle East. Iran has stressed that it sees the US military presence in Iraq as a serious threat to its security. More than 140,000 US troops are in Iraq - with more expected as part of a stepped-up Baghdad security operation.