Legalization of marijuana in the District of Columbia will go ahead early on Thursday despite a warning from congressional officials that the new standards are unlawful, Mayor Muriel Bowser said.

She noted that voters in the U.S. capital last year overwhelmingly approved Initiative 71, which lets the heavily Democratic city join Washington state, Alaska and Colorado in making marijuana legal for recreational use.

"Our government is prepared to implement and enforce Initiative 71 in the District of Columbia," Bowser, a Democrat, told a news conference flanked by council members, Police Chief Cathy Lanier and city Attorney General Karl Racine.