LONDON (Reuters) - Canadian Prime Minister Mark Carney has criticised Britain's invitation to Donald Trump for a second state visit, saying it undermined his government's effort to project a united front against the U.S. president's talk of annexing Canada.

Since taking office in January, Trump has repeatedly said he wants Canada to become the 51st U.S. state, a suggestion that has angered Canadians and left Britain trying to tread a fine line between the two North American countries.