Washington has turned down Pakistan's proposal to swap US official Raymond Davis, who shot dead two men in Lahore, with Aafia Siddiqui, a Pakistani scientist who is serving a prison term in US for killing marines in Afghanistan, it was reported here.Diplomatic Sources told the Dawn in Washington that Islamabad had taken up the proposal at "the highest level" in the Obama administration but was informed that this was "a non-starter".Washington told Islamabad that they would not trade Siddiqui with Davis as "these were two different cases".Davis, an official with a US diplomatic mission in Lahore, was arrested Jan 27 after he shot dead two youths on a motorcycle. He claimed he acted in self-defence as the armed youngsters were trying to rob him. His arrest has sparked a diplomatic crisis and strained relations between the US and Pakistan.Islamabad proposed that Siddiqui be taken to Pakistan, where she would serve the remainder of her sentence in a prison or under house arrest, the media report said Tuesday.Aafia is a Pakistani scientist, who was arrested on charges of having links with Al-Qaeda and has been sentenced by a New York court on charges of shooting US marines at Bagram airbase in Afghanistan.The other proposals taken up by Pakistan regarding the Davis case include the US government paying reparations to the victims' families who can pardon Davis.

"But on Aafia Siddiqui, the Americans are showing no leniency," the source was quoted as saying."They have informed Pakistan that they are not even going to pursue it."