"Pirate attacks in the waters off the Horn of Africa, including those on U.S.-flagged vessels, have brought continued U.S. and international attention to the long-standing problem of piracy in the region. The United States has been an active participant in piracy interdiction and prevention operations focusing on the Horn of Africa region. As part of piracy interdiction operations, the U.S. military has detained individuals accused of acts of piracy against U.S.-flagged vessels. In some instances these individuals have been released to return to land, while others have been brought to the United States for criminal prosecution in the federal courts. The U.S. Constitution gives Congress the power 'To define and punish Piracies and Felonies committed on the high seas, and Offenses against the Law of Nations.' Since 1819, U.S. law has defined piracy not as a specific act, but rather 'as defined by the law of nations.' Supreme Court decisions have upheld Congress's power to define piracy in terms of the law of nations. Contemporary international agreements, including the Convention on the High Seas, the United Nations Convention on the Law of the Sea (UNCLOS), and the Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation (SUA Convention) address piracy. The United States is party to two of the agreements, and the third (UNCLOS) is generally accepted as reflecting customary international law."
CRS Report for Congress, R41455