US President Donald Trump said in a Truth Social post on Sunday that representatives are going to Islamabad, Pakistan, "tomorrow night" for Iran negotiations.

"We are 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," Trump wrote.

Iran and the United States on Sunday accused each other of breaching the ceasefire.

Iranian Foreign Ministry spokesman Esmaeil Baghaei said the US so-called "blockade" of Iran's ports and coastlines violated the ceasefire, calling it "unlawful and criminal."

Meanwhile, Trump has accused Iran of committing a "serious violation" of the ceasefire but still thinks he can get a peace deal, according to ABC News reporter Jonathan Karl. Karl wrote on X on Sunday that Trump told him so.  

On the peace deal, Trump told Karl: "It will happen. One way or another. The nice way or the hard way. It's going to happen. You can quote me," according to Karl's X post.

(With input from agencies)