"The United States was not involved in this operation, and we had no advanced warning," Deputy Pentagon Press Secretary Sabrina Singh told journalists.

Defense Secretary Lloyd Austin -- who is returning from a trip to London -- spoke with his Israeli counterpart Yoav Gallant "as the operation was already underway," she said.

"We're still pulling for more details and trying to understand the operation itself," Singh added.

A US official, speaking on condition of anonymity, said the Israelis "told the US government they were taking military action once the operation was already ongoing and they had planes in the air," adding: "We had no advanced knowledge of this."

President Joe Biden has been briefed on the situation, the White House said.

The Israeli military said it carried out "a precise strike on the central headquarters" of Hezbollah on Friday, while leading Israeli television networks reported that the group's leader Hassan Nasrallah was the target.

"Sayyed Nasrallah is fine," a source close to Hezbollah said.

Since last week, a series of Israeli strikes have hit the southern Beirut suburbs, targeting senior Hezbollah commanders.