Tehran, Iran - US forces carried out strikes against Iran for a fourth day in a row on Tuesday and reimposed a naval blockade to prevent ships from sailing to or from the country's ports.

While President Donald Trump backtracked on his threat to heavily tax ships passing through the Strait of Hormuz, he warned he would expand US strikes on Iran next week to target power plants and bridges if Tehran does not agree to a deal.

"Next week it gets really bad for them because next week comes the power plants. Next week comes the bridges," Trump said in an interview on Fox News.

"We're going to knock out all their power plants. We're going to knock out all their bridges unless they get to the table and negotiate."

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US Central Command (CENTCOM) said the latest strikes were aimed at "degrading Iranian capabilities used to attack commercial shipping" in the strait, the key shipping channel for Gulf oil and gas where Tehran has repeatedly carried out attacks on civilian vessels.

Iranian state media reported explosions near the port city of Bandar Abbas, on the Gulf island of Qeshm near the Strait of Hormuz, and other locations.

State news agency IRNA later said that Iranian forces launched a drone attack on a military base in Jordan that hosts American warplanes.

The renewed US naval blockade came into force at 2000 GMT – an hour after the US strikes began – with a senior Iranian official saying the move effectively wrecked a deal struck with Washington to pause the conflict for peace talks.

Deputy Foreign Minister Kazem Gharibabadi said the US decision to renew the blockade "has, in a way, dismantled the Islamabad memorandum."

Admiral Brad Cooper, head of CENTCOM, said in a statement Tuesday that over the past week, "Iran has intentionally targeted civilians across the region by attacking seven commercial ships, resulting in nearly a dozen civilian crew members killed, missing, or injured."

"US forces are holding Iran accountable for unwarranted aggression that continues to endanger innocent lives," he added.

Iran had earlier Tuesday said a previous round of US strikes targeted Qeshm, while local authorities also said US forces struck "four points" in Bushehr – which hosts Iran's only civilian nuclear power plant – as well as an Iranian border area near Iraq and Kuwait.