? Denmark will investigate claims that the CIA secretly used an airport on the Nordic country's remote Arctic territory of Greenland to transport prisoners in the U.S. war on terror, the prime minister said Thursday. Denmark , like many other European countries, began investigating reports in 2005 that the U.S. intelligence agency quietly touched down on their territory as part of the CIA's so-called 'extraordinary rendition' program. Human rights groups have criticized the practice, in which suspects are transported for interrogation to countries outside the U.S. for interrogation.?