The size of the government's "no fly" list, or people who are banned from flying to or within the United States has more than doubled in the past year, says an AP report.

The no-fly list jumped from about 10,000 known or suspected terrorists one year ago to about 21,000, according to government figures provided to the AP. Most people on the list are from other countries; about 500 are Americans.

According to the AP report, a person doesn't have to be considered only a threat to aviation to be placed on the no-fly list. People who are considered a broader threat to domestic or international security or who attended a terror training camp also are included. As agencies complete the reviews of their files, the pace of growth is expected to slow, the report said.

While the list is secret, says the report, it is subject to continuous review to ensure that the right people are on it and that the ones who shouldn't be on it are removed.