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The United States has spent a record of at least $17.9 billion on military aid to Israel since the war in Gaza began and led to escalating conflict around the Middle East, according to a report for Brown University's Costs of War project, released on the anniversaryÌýof Israel's military operation in the Palestinian territory.

An additional $4.86 billion has gone into stepped-up US military operationsÌýin the region since October 7, researchers said in findings first provided to The Associated Press. That includes the costs of a Navy-led campaign to quell strikes on commercial shipping by Yemen's Houthis, who are carrying them out in support of Hamas.

The report - completed before Israel opened a second front in Lebanon in late September -Ìýis one of the first tallies of estimated US costs as the Biden administration backs Israel in its warsÌýin Gaza and Lebanon.

The financial toll is on top of the cost in human lives: Israel's offensive in Gaza has killed nearly 42,000 people, according to the territory's Health Ministry, where else more than 2,000Ìýpeople in Lebanon have been killed since Israel greatly expanded its strikes in that country in late September .

The financial costs were calculated by Linda J. Bilmes, a professor at Harvard's John F. Kennedy School of Government, who has assessed the full costs of US wars since the September. 11, 2001, attacks, and fellow researchers William D. Hartung and Stephen Semler.

Here's a look at where some of the US taxpayer money went:

Israel - a protege of the United States since its 1948 founding - is the biggest recipient of US military aid in history, getting $251.2 billion in inflation-adjusted dollars since 1959, the report says.

Even so, the $17.9 billion spent since October 7 last year, in inflation-adjusted dollars, is by far the most military aid sent to Israel in one year. The US committed to providing billions in military assistance to Israel and Egypt each year when they signed their 1979 US-brokered peace treaty, and an agreement since the Obama administration set the annual amount for Israel at $3.8 billion through 2028.

The US aid since the Gaza war started includes military financing, arms sales, at least $4.4 billion in drawdowns from US stockpiles and hand-me-downs of used equipment.

Much of the US weapons delivered in the year were munitions, from artillery shells to 2,000-pound bunker-busters and precision-guided bombs.

Expenditures range from $4 billion to replenish Israel's Iron Dome and David’s Sling missile defense systems to cash for rifles and jet fuel, the study says.

Unlike the United States' publicly documented military aid to Ukraine, it was impossible to get the full details of what the US has shipped Israel since last October 7, so the $17.9 billion for the year is a partial figure, the researchers said.

They cited Biden administration "efforts to hide the full amounts of aid and types of systems through bureaucratic maneuvering".

Funding for the US ally during a war that has exacted a heavy toll on civilians has divided Americans during the presidential campaign. But support for Israel has long carried weight in US politics, and Biden said Friday that "no administration has helped Israel more than I have".

The Biden administration has bolstered its military strength in the region since the war in Gaza started, aiming to deter and respond to any attacks on Israeli and American forces.

Those additional operations cost at least $4.86 billion, the report said, not including beefed-up US military aid to Egypt and other partners in the region.

The US had 34,000 forces in the Middle East on October 7. That number rose to about 50,000 in August when two aircraft carriers were in the region, aiming to discourage retaliation after a strike attributed to Israel killed Hamas political leader Ismail Haniyeh in Iran. The total is now around 43,000.

The number of US vessels and aircraft deployed - aircraft carrier strike groups, an amphibious ready group, fighter squadrons, and air defense batteries - in the Mediterranean, Red Sea and Gulf of Aden has varied during the year.

The Pentagon has said another aircraft carrier strike group is headed to Europe very soon and that could increase the troop total again if two carriers are again in the region at the same time.

The US military has deployed since the start of the war to try to counter escalated strikes by the Houthis,Ìýan armed faction that controls Yemen's capital and northern areas, and has been firing on merchant ships in the Red Sea in solidarity with Gaza. The researchers called the $4.86 billion cost to the US an "unexpectedly complicated and asymmetrically expensive challenge".

Houthis have kept launching attacks on ships traversing the critical trade route, drawing US strikes on launch sites and other targets. The campaign has become the most intense running sea battle the Navy has faced since World War II.

"The US has deployed multiple aircraft carriers, destroyers, cruisers and expensive multimillion-dollar missiles against cheap Iranian-made Houthi drones that cost $2,000," the authors said.

Just Friday, the US military struck more than a dozen Houthi targets in Yemen, going after weapons systems, bases and other equipment, officials said.

The researchers' calculations included at least $55 million in additional combat pay from the intensified operations in the region.