Iran's supreme leader says any US attack would spark regional war

Tensions are rising in the Middle East as US President Donald Trump weighs a possible military strike against Iran, if Tehran refuses to negotiate on a nuclear deal.

The Islamic Republic also planned a live fire military drill for Sunday and Monday in the strategic Strait of Hormuz, with its army chief saying the country is ready for war.

Iran's Supreme Leader Ali Khamanei warned a US attack would trigger a regional war.

Iran's Supreme Leader Ayatollah Ali Khamanei visiting the grave of his predecessor Ruhollah Khomeini, a significant gesture by a man who expects to be an assassination target for any US attack.

A US warship docking at an Israeli port. And reports of planned Iranian navy drills in the Strait of Hormuz. The drumbeats of war are starting to be heard in the region.

US President Donald Trump is still coy even amid reports that Saudi Arabia's defence minister says Tehran will be emboldened if Washington backs off from a strike.

On Air Force One, a reporter asked Trump for an update on his plans for Iran.

"I mean, I certainly can't tell you that, but we do have very big, powerful ships heading in that direction, as you know," Trump replied. "I can't tell you, you know. But I hope they negotiate something that's acceptable."

He was also asked about a reported comment from Saudi Arabia's defence minister, who said if the US backs off from a strike that will only embolden Tehran.

Trump responded: "Well, some people think that and some people don't. And if you could make a negotiated deal that would be satisfactory with no nuclear weapons, they should do that. But I don't know that they will. But they are talking to us, seriously talking to us."

Tehran remains calm with Iran saying they are ready for any scenario.

Reports from some online independent media say the US offered Iran a tit-for-tat deal in which they would conduct a strike with minimal damage and Tehran could respond with a similar, symbolic attack.

Iran reportedly rejected the deal, saying any attack on its territory would spark all-out war.

Iran's army commander-in-chief said on television that they are at a high level of military and defensive readiness, closely watching their enemies' movements and have their fingers on the trigger.

He warned that the security of the US forces, the region and the "criminal Zionist regime" of Israel are in danger.

A US Navy aircraft carrier, several missile-equipped destroyers and shallow-water-capable littoral combat ships have been deployed to the waters around Iran.

Meanwhile, an explosion in an apartment building on Saturday in Iran's port city of Bandar Abbas was because of a gas leak, officials said.

The blast killed a four-year-old girl as local media footage showed what it said was a security force member being carried out by rescuers. At least 14 others were injured.