Two U.S. senators have introduced an amendment to the 2017 defense bill that would limit sales of U.S. bombs to Saudi Arabia until the country takes steps to mitigate the civilian suffering in the war against Yemen's Houthi rebels.

The amendment, introduced by Sen. Chris Murphy, D-Conn., and co-sponsored by Sen. Rand Paul, R-Ky., would also halt arms sales to Saudi Arabia until the country can show it's made a concerted effort to combat terrorist organizations like al-Qaida and ISIS. The amendment calls on the Saudis to take "all feasible precautions" to reduce the killing of civilians and civilian facilities in Yemen in accordance with international law.

The United States sold $20 billion in arms to Saudi Arabia in 2015 alone, according to Human Rights Watch.

A "small number" of U.S. troops have been deployed to Yemen to support government forces, Pentagon officials said in May.

Speaking on the Senate floor Wednesday, Murphy decried the "very dangerous and catastrophic war inside Yemen," a campaign that Saudi Arabia against Shiite rebels since March 2015.

The amendment places "very reasonable conditions" on a campaign that has killed 3,000 civilians, Murphy said.

The capital city of Yemen, Sana'a, has been without electricity or running water for more than a year, he said, and 80 percent of the population is wholly dependent on humanitarian relief.

Murphy said the United States is part of a coalition bombing campaign that has destroyed schools and hospitals.

"There have been multiple reports...of U.S.-made cluster bombs being used in or near civilian populations," he said. "It would not happen without U.S. participation."

Beyond U.S. munitions, American intelligence agencies are providing the information used for the bomb targeting, and U.S. tankers are conducting in-flight refueling for those aircraft.

"The U.S. is an indispensable part of this coalition," Murphy said. "We've got to add some conditions."

Murphy conceded that he likely could not garner support for a temporary or permanent halting of the campaign in Yemen, but said the amendment offers "common sense conditions."

"Try to kill less civilians instead of more civilians," Murphy said.