OTTAWA -- Prime Minister Justin Trudeau is promising close collaboration with the premiers throughout negotiations to overhaul the North American Free Trade Agreement.

In return, the provincial leaders are pledging a united front to vigorously defend Canada's interests in the talks, which are set to start Aug. 16.

The exchange of promises came in a conference call Trudeau held Thursday with provincial and territorial leaders.

Canada's ambassador to the United States, David MacNaughton, also participated.

A summary of the call released by the Prime Minister's Office says the first ministers agreed to continue working closely together to ensure the message about the value of NAFTA and the trade relationship with Canada is understood by key decision-makers in the U.S.

Federal and provincial leaders, ministers and officials have for months been conducting a full-court press in the U.S. to make that case with American state and federal legislators and business leaders.