US President Donald Trump said Monday he will hold off on attacking Iranian power plants for five days after "very good" talks with Tehran, an abrupt shift that immediately eased pressure on rattled markets.

Hours before the expiration of his two-day ultimatum -- in which he threatened to "obliterate" Iran''s power infrastructure if it did not reopen the strategic Strait of Hormuz -- Trump suddenly reported with little detail that diplomacy was underway, after he earlier shunned talks.

In a social media post characteristically in all capital letters and containing typographical errors, Trump said the United States and Iran "have had, over the last two days, very good and productive conversations regarding a complete and total resolution of our hostilities in the Middle East."