DONALD TRUMP has threatened to block the opening of a new Canadian-built and funded bridge across the Detroit river.

The increasingly unstable US president is demanding that Canada turn over at least half of the ownership of the bridge and agree to other unspecified demands.

“We will start negotiations immediately. With all that we have given them, we should own, perhaps, at least one half of this asset,” Mr Trump complained in a lengthy social media post on Monday, adding that his country would get nothing from the bridge and that Canada had not used US steel to build it.

The Gordie Howe International Bridge, named after a former Canadian hockey star who played for the Detroit Red Wings, had been expected to open early this year.

It’s unclear how the US president would seek to block the Canadian-funded bridge from opening. 

Neither the White House or the Canadian embassy in Washington immediately responded to requests for comment.

While Canada paid for the project, the bridge will be operated under a joint ownership agreement between Michigan and Canada, said Stacey LaRouche, press secretary to state Governor Gretchen Whitmer.

Ms LaRouche said the bridge was “going to open one way or another and the governor looks forward to attending the ribbon-cutting.”