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US Defence Secretary Lloyd Austin arrived in Israel on Friday to meet Prime Minister Benjamin Netanyahu and members of his cabinet.
Mr Austin is expected to reaffirm Washington's “unwavering support” and ensure Israel has what it needs to defend itself, the Pentagon said.
He will also inspect some of the security assistance the US has delivered to its ally.
The trip comes as Washington works to help Israel respond to Saturday's Hamas attacks that triggered a wave of violence that has killed thousands of people in Gaza and Israel.
Mr Austin “is looking forward to speaking in depth with Israeli leaders about their operational planning and their objectives for this conflict”, a senior US defence official told reporters.
Mr Austin's trip will come a day after Secretary of State Antony Blinken visited Israel in a show of solidarity.
Hamas militants smashed through the border fence enclosing the Gaza Strip at the weekend and went on a horrific rampage, attacking civilians in southern Israel as thousands of rockets flew overhead.
The Israeli military's response has so far been to bomb large parts of Gaza in retaliatory strikes that have killed hundreds of people, many of them children.
So far, the US has sent an aircraft carrier strike group to the Eastern Mediterranean, deployed warplanes to the region and is rushing munitions, including small diameter bombs, to Israel, the official said.
At the White House earlier on Thursday, National Security spokesman John Kirby said there was no intention to send US troops into Israel to assist in any military operations.
Speculative media reports have suggested the Pentagon is considering sending US special operations forces to Israel to help extract American hostages held by Hamas.
“There is no intention, no plan and, frankly, no desire by the Israelis for US combat troops to be involved in this conflict,” National Security Council spokesman John Kirby told reporters.
But the senior defence source said there were “military personnel” attached to the US embassy already in Israel “providing advice on hostage recovery, which obviously is a really significant concern and priority for both the United States and Israel”.
When asked if Washington would put any restrictions put on how Israel uses US-provided weapons in Gaza, Mr Kirby said: “I won’t speak about that for Israeli operational security reasons.”
The US often places restrictions on weapons sales to countries if there are concerns they will be used against civilians.