Khamenei welcomes Obama's "window of opportunity" (AP) TEHRAN, Iran - Iran's top leader Thursday welcomed comments by President Barack Obama advocating diplomacy and not war as a solution to Tehran's nuclear ambitions, a rare positive signal in long-standing hostile transactions between Tehran and Washington. The report on Iran's state television quoted Ayatollah Ali Khamenei as praising a recent statement by the U.S. president saying he saw a "window of opportunity" to use diplomacy to resolve the nuclear dispute. Khamenei, who has final say on all state matters in Iran, told a group of clerics: "This expression is a good word. This is a wise remark indicating taking distance from illusion. It is one of the rare cases in which Iran's top leader praised an American leader. Kerry: Romney's behavior on Iran "irresponsible" Romney: Obama "dawdled" on Iran Obama to GOP rivals: War in Iran "not a game" Washington and Tehran have had no diplomatic relations since the 1979 takeover of the U.S. Embassy in Tehran by Iranian students who took American diplomats hostage. Both the U.S. and Israel fear Iran's nuclear program is aimed at building a nuclear weapon, while Iran says its nuclear activities are geared toward peaceful purposes such as power generation. But the U.S. and Israel have differed over how to deal with the nuclear problem. Israel has said military action should be considered to stop the Iranians. President Barack Obama told visiting Israeli Prime Minister Benjamin Netanyahu earlier this week that diplomacy must be given more time. On Tuesday, the American president said diplomacy can still resolve the nuclear crisis and accused his Republican critics of "beating the drums of war." Mr. Obama added that the Iranians need to show how serious they are about resolving the crisis. He said there are steps the Iranians can take "that are verifiable" and will allow the country to be "in compliance with international norms and mandates." AP: Iran may have cleaned up nuke work IAEA members struggle to find unity on Iran nukes But Khamenei had criticism for Mr. Obama as well. The Iranian leader said the economic sanctions pushed by the U.S. and other nations as a way to get Iran to alter its nuclear program would fail. He said the U.S. president has continued a policy of wanting the Iranian nation to ..."bow through imposing sanctions." Khamenei said resorting to the sanctions was a sign of misunderstanding and an unrealistic approach by the U.S. toward the Iranian nation. The Iranian leader warned that the misunderstanding will damage American leaders: "It will lead their calculations to failure." Khamenei's response focused on the U.S., but concerns over Iran's nuclear program extend beyond Washington and Tel Aviv. Six world powers on Thursday urged Iran to answer questions about suspicions it is working on nuclear weapons, but stressed that diplomacy was the way forward, in a carefully worded statement that reflected Western sensitivity to Russian and Chinese concerns about being too harsh on Tehran. The six urged Iran to open its Parchin military site to International Atomic Energy Agency perusal, amid reports that Tehran might be cleaning it of evidence of nuclear arms related experiments - a request echoed by other speakers at the 35-nation IAEA board meeting. While also stressing the diplomacy was the key to resolving tensions over Iran's nuclear program, a European Union statement was stronger than that from the six powers, noting "regret" of Iran's lack of response to international concern. Concerns about Parchin are high. Diplomats who spoke to The Associated Press on Wednesday based their assessment on satellite images of the Iranian military facility they said appeared to show trucks and earth-moving vehicles, indicating an attempted cleanup of radioactive traces. Two of six diplomats said their information reveals that Iran had experimented with a test version of a neutron trigger at the site used to set of a nuclear blast - information not previously made public. The IAEA has already identified Parchin as the location of suspected nuclear weapons-related testing. IAEA expert teams trying to probe the suspicions of secret weapons work by Iran tried - and failed - twice in recent weeks to get Iranian permission to visit Parchin. Tehran said on Monday that such a visit would be granted. But it said that a comprehensive agreement outlining conditions of such an inspection must first be agreed on - a move dismissed by a senior international official familiar with the issue as a delaying tactic. He requested anonymity because his organization does not authorize him to speak publicly on confidential IAEA matters. The EU statement was sprinkled with diplomatic code words meant to convey strong criticism of Iran's defiance of international demands that it lower tensions levels by compromising on its nuclear activities. "We deeply regret" Iran's lack of efforts to dispel international suspicions, said the statement, urging it "to enter without delay" into a dialogue with the agency that leads quickly to diminishing fears of a secret nuclear-weapons agenda on the part of Tehran. German Foreign Minister Guido Westerwelle was even more direct. He said Germany and the five other world powers trying to engage Tehran on its nuclear program were sending "a clear message to Iran to finally end its non-cooperation and to clear up all the justified concerns about the purpose of its atom program transparently and logically."