US President George W. Bush has sent a letter to North Korean leader Kim Jong Il, the nation's official news agency said Thursday, in the latest sign of warming ties between the former enemies. US nuclear envoy Christopher Hill delivered the message to North Korean Foreign Minister Pak Ui Chun during his recent trip to Pyongyang, the Korean Central News Agency said. KCNA did not give further details about the letter. If confirmed, the letter would be unprecedented move by Bush. Bush once called North Korea part of an "axis of evil" along with Iran and pre-war Iraq, and halted direct US talks with the communist country after he came into office, before later allowing a resumption of negotiations.