President Donald Trump said in a post on his social media platform Sunday afternoon that the U.S. Navy had attacked an Iranian-flagged cargo ship in the Gulf of Oman and that U.S. Marines have taken custody the vessel.

“Today, an Iranian-flagged cargo ship named TOUSKA, nearly 900 feet long and weighing almost as much as an aircraft carrier, tried to get past our Naval Blockade, and it did not go well for them,” Trump said in the post.

If true, it would appear to be the first instance of the U.S. attacking and seizing a merchant vessel since it instituted the blockade of Iranian ports.

“The U.S. Navy Guided Missile Destroyer USS SPRUANCE intercepted the TOUSKA in the Gulf of Oman, and gave them fair warning to stop," Trump wrote. "The Iranian crew refused to listen, so our Navy ship stopped them right in their tracks by blowing a hole in the engine room.”

The president further wrote that "U.S. Marines have custody of the vessel," which he said is "under U.S. Treasury Sanctions because of their prior history of illegal activity. We have full custody of the ship, and are seeing what’s on board!"

The move comes after Joint Chiefs Chairman Gen. Dan Caine warned that the U.S. would actively enforce the blockade on Iranian-flagged vessels around the globe.

"In addition to this blockade, the joint force through operations and activities in other areas of responsibility, like the Pacific area of responsibility under the command of Admiral Paparo, will actively pursue any Iranian-flagged vessel or any vessel attempting to provide material support to Iran. This includes Dark Fleet vessels carrying Iranian oil," Caine said in a Pentagon press conference Thursday.

-ABC News' Nicholas Kerr

As Tehran asserts that it will not participate in a second round of in-person talks with U.S. negotiators in Islamabad, Pakistan, on Monday unless the naval blockade on Iranian ports is lifted, President Donald Trump is claiming that a peace deal is almost complete.

"I feel fine about it. The concept of the deal is done. I think we have a very good chance to get it completed," Trump told Axios in an interview on Sunday.

The president offered no details regarding what was in the deal.

Trump's comments to Axios were published just hours after he threatened to bomb all of Iran's power plants and bridges if the Iranians don't sign the deal.

“If the deal isn’t done, the deal that we made, then I’m going to take out their bridges and their power plants," Trump told Fox News in a separate interview. “If they don’t sign this thing, the whole country is going to get blown up.”

The president told ABC News' Jonathan Karl something similar Sunday.

"It’s going to be very good," Trump said. "They are either going to do it or they are going to have problems. We’ll see what happens."

The present ceasefire agreement is set to expire on Wednesday.

-ABC News' Nicholas Kerr

President Donald Trump said Sunday morning that the entire country of Iran would get “blown up” if leaders there don’t sign a deal with the U.S.

"If they don't sign this deal, the whole country is going to get blown up," Trump told Fox News, shortly after he wrote on his social media platform that talks would resume in Islamabad on Monday.

The president later told The New York Post that his advisers, special envoy Steve Witkoff and Jared Kushner, would be heading to Islamabad on his behalf.

The president did leave open the possibility that he could travel to Islamabad at some point, but gave no indication when.

“I would say maybe at a little bit later date. We have to see how it works out tomorrow,” he said.

-ABC News' Nicholas Kerr

President Donald Trump said in a Sunday post on his social media platform that he was dispatching his representatives to Islamabad, Pakistan, for another round of peace talks with Iran on Monday night.

"My Representatives are going to Islamabad, Pakistan – They will be there tomorrow evening, for Negotiations," the president wrote.

He also blasted Iran for allegedly firing on vessels transiting the Strait of Hormuz Saturday, which he called a “total violation” of the ceasefire, and urged Iran to make a deal with the U.S. or face strikes on power plants and bridges inside the country.

“We’re offering a very fair and reasonable DEAL, and I hope they take it because, if they don’t, the United States is going to knock out every single Power Plant, and every single Bridge, in Iran. NO MORE MR. NICE GUY!" Trump wrote. "They’ll come down fast, they’ll come down easy and, if they don’t take the DEAL, it will be my Honor to do what has to be done, which should have been done to Iran, by other Presidents, for the last 47 years. IT’S TIME FOR THE IRAN KILLING MACHINE TO END!"

Trump made a similar threat against Iran on Easter weekend, posting on his social media platform that he would bomb Iran's power plants and bridges and send the country "back to the Stone Ages, where they belong" if they didn't then open the Strait of Hormuz to shipping traffic.

The current ceasefire agreement is set to expire on Wednesday.

-ABC News' Nicholas Kerr

Iran's supreme leader, Ayatollah Mojtaba Khamenei, said in a statement on Saturday that his country was "now courageously defending the land, water, and flag that belong to it."

Khamenei, who has not been seen publicly since the beginning of the war, said in the statement that Iran in fighting against the U.S. and Israel was "battling against the two leading armies of disbelief and Arrogance."

"And the Islamic Army has exposed those armies' weakness and abjectness to the world," the statement said. "In the same way that its drones strike the US and the Zionist murderers like lightning, its valiant navy is also ready to inflict new bitter defeats on its enemies."