TEHRAN/WASHINGTON -- Iran and the United States on Sunday accused each other of ceasefire breach.

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, US President Donald Trump has accused Iran of committing a "serious violation" of the ceasefire, according to Jonathan Karl, ABC News' chief Washington correspondent, who wrote on X on Sunday that Trump told him so.

Karl added that Trump told him that an agreement would be reached "one way or another. The nice way or the hard way."

In his Truth Social post on Sunday morning, Trump said the US representatives are going to Islamabad on Monday for a new round of negotiations.

The United States is "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 added.

Shipping through the Strait of Hormuz remained at a standstill on Sunday after the United States imposed a naval blockade on Iran, prompting Iran to reassert control over the strategic waterway.