The French government is pressing the US Department of Homeland Security to release the 85-year-old French widow of a military veteran from immigration custody after she was detained earlier this month.

US Immigration and Customs Enforcement agents detained Marie-Thérèse Ross in Alabama on April 1 after she overstayed her 90-day visa, according to DHS. Ross is now being held at a federal immigration detention facility in Louisiana.

Ross is among the thousands of people targeted by the Trump administration's mass deportation agenda that has detained the spouses of US soldiers and military veterans who previously received greater leniency under scrapped policies.

Ross married Alabama resident William Ross in April last year, Calhoun County marriage records show. Ross died in January, according to an obituary from his family, which says he was a former captain in the US Army.

A lawyer who is representing Ross in a separate legal matter did not immediately respond to a request for comment. Ross' family did not respond to requests for comment.