Citing humanitarian concerns regarding Saudi Arabia's ongoing war against Houthi rebels in Yemen, U.S. lawmakers on Monday asked the White House to delay a proposed $1.15 billion weapons sale to the kingdom.

The letter, signed by 64 members of Congress, asks the Obama administration to walk back the Aug. 8 approval of the sale, which would include replacing tanks destroyed in the Yemen campaign.

"This military campaign has had a deeply troubling impact on civilians," the letter from Rep. Ted Lieu, D-Calif., states.

The letter cites Amnesty International's documentation of at least 33 unlawful airstrikes by the kingdom across Yemen, missions that "deliberately targeted civilians and civilian facilities, such as hospitals, schools, markets, and places of worship."

"The attacks may amount to war crimes," the letter cautions.

The U.N. Office of the High Commissioner for Human Rights has found that 3,704 civilians, including 1,121 children, have been killed during the conflict, with 2.8 million Yemenis displaced in a war that has left 83 percent of the population dependent on humanitarian assistance for survival, Lieu's letter states.

Past Congressional concerns about the Saudi war in Yemen have not been addressed, according to the letter.

The letter cites an October correspondence where Congressional members urged the White House to pursue greater efforts to avoid civilian casualties in the conflict.

In June, a bipartisan assembly of lawmakers voted to block the transfer of cluster bombs to Saudi Arabia after reports emerged of their use on Yemeni civilians.

"Any decision to sell more arms to Saudi Arabia should be given adequate time for full deliberation by Congress," the letter states.

The letter also voices concern about the White House's timing regarding Congressional notification of the latest Saudi sale during the August recess.

"We are not aware of any compelling reason why Congressional approval of the sale could not be postponed to allow for meaningful Congressional debate on this issue that has major implications for both civilians in Yemen as well as our national security," the letter states.

With General Dynamics Land Systems as the principal contractor, the sale would involve up to 153 M1A1/A2 tank structures for conversion to 133 M1A2S Saudi Abrams tanks and 20 battle damage replacements for the existing fleet.

It also includes 153 M2 .50 caliber machine guns, 266 7.62 mm M240 machine guns, 153 M250 smoke grenade launchers, 20 M88A HERCULES armored recovery vehicle structures for conversion to 20 M88A1/A2 HERCULES vehicles, 169 AN/VAS-5 Driver Vision Enhancer-Abrams, 133 AN/PVS-7B night vision devices, 4,256 rounds of M865 training ammunition and 2,394 rounds of M831AI training ammunition.

Also included in the potential sale are M1A1I/2 tank and M88A1/A2 armored recovery vehicle overhaul, conversion and refurbishment services, special tools and test equipment, basic issue items, program management support, verification testing, system technical support, advanced gunnery training system, deployable advanced gunnery training system, transportation, binoculars, camouflage netting, spare and repair parts, communications equipment, personnel training and training equipment, tool and test equipment, repair and return, publications and technical documentation, quality assurance team, U.S. government and contractor engineering, technical and logistics support services, as well as other related logistics and program support elements.