The US has prepared for what could be significant attacks by Iran or Iran-aligned groups in the Middle East as soon as this week, White House National Security Council spokesperson John Kirby said.

Kirby said on Monday that the US had increased its regional force posture and shared Israel's concerns about a possible Iranian-backed attack after Iran and Palestinian resistance group Hamas accused Israel of carrying out the assassination of a Hamas leader in Tehran last month.

"We share the same concerns and expectations that our Israeli counterparts have with respect to potential timing here. Could be this week," Kirby told reporters.

"We have to be prepared for what could be a significant set of attacks," he said.

Israel has not publicly acknowledged killing Haniyeh, but the Washington Postreported on August 6 that Tel Aviv informed US officials it was behind the assassination of the Hamas politburo leader in Iranian capital Tehran — an admission that was met with "surprise and outrage".

Iran has since vowed retaliation against Israel.

"We obviously don't want to see Israel have to defend itself against another onslaught, like they did in April. But, if that's what comes at them, we will continue to help them defend themselves," Kirby said.

The Pentagon said on Sunday that Defense Secretary Lloyd Austin had ordered the deployment of a guided missile submarine to the Middle East and for the Abraham Lincoln carrier strike group to accelerate its deployment to the region.

The threat of an Iranian retaliation comes as Israeli forces pressed on with attacks near the southern Gaza city of Khan Younis on Monday amid an international push for a deal to halt fighting in Gaza and prevent a slide into a wider regional conflict with Iran and its proxies.