It was the second such action this week, as the Trump administration ramps up pressure on Tehran.
The seizure was the latest U.S. effort to squeeze Iran’s oil-reliant economy, and came days after the Navy boarded an Iranian cargo ship near the Strait of Hormuz.
Marines are searching thousands of containers aboard the Touska, an Iranian cargo ship that the Navy disabled and seized on Sunday.
In a letter, the 11 senators questioned the defense secretary’s decision to gut programs intended to protect civilians and said his orders endangered U.S. troops.
The U.S. blockade of shipments through the Strait of Hormuz would last “for as long as it takes,” the defense secretary said.
The G.O.P. narrowly blocked a Democratic war powers resolution, but a senior Republican suggested that backing for the conflict is not open-ended and could wane as a statutory deadline approaches in weeks.
House lawmakers had been scheduled to hear testimony next week from the head of military operations in the Middle East, but the Republican majority postponed the hearing until late May.
After careening from one diplomatic extreme to another, President Trump finds himself with a fragile deal that is already showing signs of fraying.
President Trump knows that even if a cease-fire runs out with no final agreement on the issues dividing Washington and Tehran, the political risk of renewing hostilities is high.
President Trump said that “we have already met and exceeded” his military objectives. But his goals are largely unresolved.