WASHINGTON, Dec 13 (Reuters) - The United States has helped over 900 American citizens and lawful permanent residents to leave Afghanistan and relocate to the United States since Aug. 31, after the chaotic end to the American war there, the U.S. State Department said on Monday. The United States has directly assisted 479 American citizens and 450 lawful permanent residents, in addition to their immediate families, depart Afghanistan and relocate to the United States since the end of August, the State Department said in a statement. The agency is in touch with fewer than a dozen U.S. citizens who want to leave the country, are prepared to depart and have the necessary travel documents, according to the statement. "There is no deadline for this work," the department said. The United States" two decade-long occupation of Afghanistan culminated in a hastily organized airlift in August in which more than 124,000 civilians - including Americans, Afghans and others - evacuated as the Taliban took over. But thousands of other U.S.-allied Afghans at risk of Taliban persecution were left behind.