"If Iran chooses poorly, then they will have a blockade and bombs dropping on infrastructure, power and energy," Hegseth told a news conference at the Pentagon.

US forces began blockading Iranian ports at 1400 GMT on Monday after peace talks in Pakistan ended without an agreement the previous day.

General Dan Caine, the top US military officer, said the blockade "applies to all ships, regardless of nationality, heading into or from Iranian ports."

"If you do not comply with this blockade, we will use force," said Caine, who spoke alongside Hegseth.

The general also said that Washington's forces would chase down ships in other areas that try to carry aid to Iran.

"In addition to this blockade, the joint force, through operations and activities in other areas of responsibility...will actively pursue any Iranian-flagged vessel, or any vessel attempting to provide material support to Iran," Caine said.

Hegseth meanwhile said Iranian forces are attempting to dig out equipment buried during the more than five weeks of US-Israeli strikes against the Islamic republic.

Addressing Iranian leaders directly, he said: "We know what military assets you are moving and where you are moving them to. While you are digging out -- which is exactly what you're doing, digging out of bombed out and devastated facilities -- we are only getting stronger."

"You are digging out your remaining launchers and missiles with no ability to replace them -- you have no defense industry, no ability to replenish your offensive or defensive capabilities," Hegseth said.

Admiral Brad Cooper, the head of US Central Command, which is responsible for American forces in the Middle East, said Washington is using the ceasefire to reset.

"We're rearming, we're retooling, and we're adjusting our tactics, techniques and procedures. There's no military in the world that adjusts like we do, and that's exactly what we're doing right now during the ceasefire," Cooper said.