US President Donald Trump says he has invoked the "Alien Enemies Act" in a bid to facilitate the detention and deportation of alleged members of a Venezuelan gang.



In announcing the step on Saturday, Trump said the Tren de Aragua gang is "perpetrating, attempting and threatening an invasion or predatory incursion against the territory of the United States." The group has been designated as a foreign terrorist organization.



Trump said all Venezuelan citizens 14 years of age or older who are members of this group within the United States are "liable to be apprehended, restrained, secured, and removed as Alien Enemies." An exception has been made for naturalized or lawful permanent residents.



The "Alien Enemies Act," enacted in 1798, allows the president to detain or deport the natives and citizens of an enemy nation in time of war without undergoing normal court procedures.



The law has been invoked only three times in the past. It was used to detain immigrants from Japan and elsewhere during World War Two.



Trump's invocation of the act is causing controversy in the United States. The influential rights group American Civil Liberties Union said that the act's previous use during wartime, including its invocation during World War Two to justify the internment of people of Japanese ancestry, has correctly drawn sustained criticism. It argued that employing the act as a way to evade domestic laws in peacetime is "fundamentally wrong."