LONDON, July 13 (Reuters) - More details are awaited after U.S. President Donald Trump said in a post that Washington was reinstating a naval blockade on Iran and would be reimbursed 20% on all cargo shipped through the Strait of Hormuz, the U.N.'s shipping agency said on Monday.

"We are aware of the post and awaiting more details," a spokesperson with the U.N.'s International Maritime Organization said.

"We have always been consistent on our stance on fees – IMO stands firmly against charging fees for passage through straits used for international navigation. There is no legal basis through which to introduce mandatory tolls simply to transit through a strait."

Trump said in a Truth Social post the process would begin immediately, but did not elaborate.