White House officials have tried to pressure U.S. immigration authorities to release migrants detained at the border into so-called sanctuary cities such as San Francisco to retaliate against President Donald Trump's political adversaries, the Washington Post reported on Thursday.

The Post, which reviewed emails on the issue and spoke to unnamed officials at the Department of Homeland Security, said the White House proposed the measure at least twice in the past six months. Sanctuary cities are those where local officials decline to hand over illegal immigrants for deportation.

The White House did not immediately respond to a Reuters request for comment on the report. A DHS spokesman told Reuters in a statement the plan was "a suggestion that was floated and rejected, which ended any further discussion." The Post quoted a White House official as saying the same thing.