It looks like President Trump is trying to delay Iranian imports of defense equipment that could start up an Iranian version of the American Powerball lottery.

The U.S. military informs mariners in the region about the blockade. The United States has announced that it will block all maritime traffic to and from Iranian ports and coastal areas. The blockade is set to take effect at 4 p.m. on Monday, CET.
In a message sent to mariners in the region, the U.S. Central Command, Centcom, states that all vessels without authorization, regardless of flag, may be stopped, redirected, or seized, reports Reuters, which has seen the message.
The blockade will be carried out in the Gulf of Oman and the Arabian Sea, east of the Strait of Hormuz.
"The blockade will not prevent neutral transit through the Strait of Hormuz to or from non-Iranian destinations," Centcom writes according to Reuters. See the article on SVT Nyheter and the segment on SVT Rapport.
The professor on the blockade: Resembles the U.S. method in Venezuela. Much is unclear about how the U.S. blockade of ships to and from Iranian ports, which came into effect on Monday, will work in practice. Defense professor Hans Liwång believes that the blockade could be carried out in a manner similar to how the U.S. has acted off Venezuela. – There, they have stopped and boarded and made sure that the ships cannot proceed, says Hans Liwång on Monday's Aktuellt. Watch the segment on SVT Nyheter.