Washington: US President Donald Trump on Thursday said all American military assets will remain deployed in and around Iran, warning of a massive escalation if a “real agreement” is not honoured.

In a post on Truth Social, Trump asserted that US forces are fully prepared for further action while emphasising that Iran must comply with longstanding conditions.

“All U.S. Ships, Aircraft, and Military Personnel, with additional Ammunition, Weaponry, and anything else that is appropriate and necessary for the lethal prosecution and destruction of an already substantially degraded Enemy, will remain in place in, and around, Iran, until such time as the REAL AGREEMENT reached is fully complied with. If for any reason it is not, which is highly unlikely, then the ‘Shootin’ Starts,’ bigger, and better, and stronger than anyone has ever seen before,” he said.

Trump further stated that key terms of the understanding include preventing Iran from acquiring nuclear weapons and ensuring free navigation through the Strait of Hormuz.

“It was agreed, a long time ago, and despite all of the fake rhetoric to the contrary - NO NUCLEAR WEAPONS and, the Strait of Hormuz WILL BE OPEN & SAFE,” he said.

He added that US forces are on standby and preparing for potential operations.

“In the meantime our great Military is Loading Up and Resting, looking forward, actually, to its next Conquest,” Trump said.

The United Nations secretary-general on Thursday warned that deadly Israeli strikes on Lebanon posed a "grave risk" to the fragile US-Iran truce, his spokesperson said in a statement.

"The ongoing military activity in Lebanon poses a grave risk to the ceasefire and the efforts toward a lasting and comprehensive peace in the region. The Secretary-General reiterates his call to all parties to immediately cease hostilities," UN chief Antonio Guterres's spokesman said.

The Lebanese health ministry reported that 182 people were killed and 890 wounded by Israeli strikes on Wednesday, with capital Beirut hit by the most violent bombardment yet since the start of the war between Israel and Hezbollah.

Lebanon was pulled into the war after the Tehran-backed militant group targeted Israel in retaliation for the US-Israel war against Iran.

While Iran and the United States agreed to a two-week ceasefire late on Tuesday, Israel insisted that Lebanon was not part of the truce.

Hezbollah responded by saying it had fired rockets towards Israel, and Iran's parliament speaker Mohammad Bagher Ghalibaf appeared to threaten the ceasefire.