The Bush administration has been flying surveillance drones over Iran for nearly a year to seek evidence of nuclear weapons programs and detect weaknesses in air defenses, according to three U.S. officials with detailed knowledge of the secret effort. The small, pilotless planes, penetrating Iranian airspace from U.S. military facilities in Iraq, use radar, video, still photography and air filters designed to pick up traces of nuclear activity to gather information that is not accessible by satellites, the officials said. The aerial espionage is standard in military preparations for an eventual air attack and is also employed as a tool for intimidation. The Iranian government, using Swiss channels in the absence of diplomatic relations with Washington, formally protested the incursions as illegal, according to Iranian, European and U.S. officials, all speaking on the condition of anonymity because of the sensitivity of the matter. A U.S. official acknowledged that drones were being used but said the Iranian complaint focused on aircraft overflights by the Pentagon. The United States, the official said, replied with a denial that manned U.S. aircraft had crossed Iran's borders. The drones were first spotted by dozens of Iranian civilians and set off a national newspaper frenzy in late December over whether the country was being visited by UFOs. The surveillance has been conducted as the Bush administration sharpens its anti-Iran rhetoric and the U.S. intelligence community searches for information to support President Bush's assertion that Tehran is trying to build nuclear weapons. [more]