The United States is advising Israel on its promised response to an Iranian missile attack, US President Joe Biden told reporters on Thursday, underscoring Washington's central role in an escalating crisis which threatens all-out war.

No military action was expected on Thursday, Biden added.

Asked if the United States would support Israeli strikes on Iranian oil facilities, Biden said: "We’re in discussion of that. I think - I think that would be a little - anyway."

The remarks were at times clipped and occurred in a series of back-and-forth questions with a group of journalists as the presidential helicopter was preparing to depart.

Biden took issue with one journalist's characterization of whether the United States will "allow" its main partner in the region to carry out an attack.

"First of all, we don’t allow Israel. We advise Israel. And there’s nothing going to happen today. We’ll talk about that later," he said.

US crude oil prices hit one-month highs and were up nearly $4 a barrel to $74 after Biden's comments.

Energy markets have been volatile as Mideast tensions have ramped up but have not reacted radically to the potential supply risks in the key Persian Gulf production area.

Iran launched around 180 missiles at Israel on Tuesday, the Israeli military said. The attack was largely repulsed with US and Western help but several missiles landed, including on an Israeli air base.

It was the biggest direct confrontation between the Islamic Republic and Jewish State and brings their rivalry which has simmered for over four decades toward the brink of war.

Biden had told reporters on Wednesday that the United States did not support a strike on Iranian nuclear sites.

State Department spokesperson Matthew Miller later on Thursday detailed further the breadth of US-Israeli contacts.

"We are also having conversations with them about the shape of that campaign, the scope of that campaign, what their targets are going to be."