President Biden's administration has approved a $735 million weapons sale to Israel, which may not please some congressional Democrats.

A source familiar with the sale confirmed to Fox News that the Biden administration sent Congress a formal notice of the sale on May 5. That date was nearly a week before Hamas, which controls the Gaza Strip and has been designated a terrorist organization by the United States, began launching massive rocket attacks into neighboring Israeli, which sparked a ferocious aerial response by Israeli forces.

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Nearly 200 Palestinians and at least 10 Israelis have been killed in the worst fighting between the two enemies in seven years.

Most of the proposed sale is for joint direct attack munitions, known by the acronym JDAMS, which transform so-called "dumb" bombs into precision guided missiles. Israel, which has purchased JDAMS in the past, has said they are used to try and avoid hitting civilians during their air strikes on densely populated Gaza.

The Biden administration's notification to Congress, first reported by The Washington Post, triggered a 15-day review process which should end later this week.

While pushing for an immediate cease-fire, the U.S. administration backs Israel's right to defend itself from attacks by Hamas. There is uniform support for the position among congressional Republicans, but a growing number of progressive Democrats in Congress is questioning Washington’s support of conservative Israeli Prime Minister Benjamin Netanyahu.

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Some lawmakers on the left are raising red flags and asking questions about the arms sale.

"The devastation in Gaza is unconscionable. We must urge an immediate ceasefire. The killing of Palestinians and Israelis must end," Sen. Bernie Sanders of Vermont tweeted on Sunday.

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The progressive champion and two-time Democratic presidential candidate emphasized: "We must also take a hard look at nearly $4 billion a year in military aid to Israel. It is illegal for U.S. aid to support human rights violations."

Fox News' Paul Steinhauser contributed to this report.