Iran and its regional allies have threatened to attack Israel in response to high-profile killings in Tehran and Beirut late last month, and Hezbollah said its recent strikes on Israel were in response to one of those assassinations.

"We continue to assess that there is a threat of attack, and we... remain well-postured to be able to support Israel's defense as well as to protect our forces should they be attacked," Pentagon spokesman Major General Pat Ryder told journalists.

On Sunday, the Israeli military said it launched air strikes on Hezbollah targets that posed an imminent threat, with around 100 fighter jets striking more than 270 targets, most of them short-range rockets aimed at northern Israel.

Hezbollah chief Hassan Nasrallah said the Israeli strikes came half an hour before his group launched more than 300 Katyusha rockets at 11 Israeli military sites, and that drones then targeted deeper inside the country, in response to the killing of senior commander Fuad Shukr in July.

Ryder said that the US was not involved in the preemptive strikes or in shooting down the projectiles, but that it did "provide some intelligence, surveillance, reconnaissance support -- ISR -- in terms of tracking incoming Lebanese Hezbollah attacks."

He also said that US Defense Secretary Lloyd Austin "has ordered the presence of two carrier strike groups to remain in the region" as part of support for Israel.

The Pentagon said last week that the USS Abraham Lincoln and accompanying destroyers had arrived in the region.

It was due to replace the USS Theodore Roosevelt, but Austin's order means both carriers will be in the Middle East for the time being.

Top US military officer General Charles "CQ" Brown meanwhile met on Monday with Israeli security officials including Defense Minister Yoav Gallant, who said that "Iran's aggression has reached an all-time high."

"To counter this, we must work together to achieve and project groundbreaking capabilities in all arenas," Gallant said, according to an Israeli statement on the meeting.

Brown is on a multi-country trip to the Middle East that has also taken him to Jordan and Egypt.