Jan 14 (Reuters) - U.S. President-elect Donald Trump said on Tuesday he will create a new department called the External Revenue Service "to collect tariffs, duties, and all revenue" from foreign sources.

Trump said in a social media post he would create the department on Jan. 20, the day he will be inaugurated as president for a second term.

"Through soft and pathetically weak Trade agreements, the American Economy has delivered growth and prosperity to the World, while taxing ourselves. It is time for that to change," the Republican said in a post on Truth Social.

"We will begin charging those that make money off of us with Trade, and they will start paying, FINALLY, their fair share."

Trump has pledged to impose big tariffs on the United States' three largest trading partners - Canada, Mexico and China - including a 25% tariff on imports from Canada and Mexico until they clamped down on drugs and migrants crossing the border.

He has also vowed impose tariffs of 10% on global imports into the United States, along with a 60% tariff on Chinese goods - duties that trade experts say would upend trade flows, raise costs and draw retaliation against U.S. exports.

The Trump transition team didn't immediately respond to a request for comment on details of how the new agency would work.