Iran's supreme leader Ayatollah Ali Khamenei condemned on Sunday US President Barack Obama for issuing what he said was a threat of a nuclear attack against the Islamic republic. "He (Obama) has implicitly threatened Iranians with nuclear weapons," Khamenei was quoted by state television as telling Iran's top military officials in Tehran. "These comments are very strange and the world should not ignore them because in the 21st century... the head of a state is threatening a nuclear attack," said the all-powerful Iranian leader. "The US president's statements are disgraceful. Such comments harm US and they mean that the US government is wicked and unreliable."