The US’s support for Israel’s bombing campaign in Gaza is facing new scrutiny in Washington following a proposed resolution by the independent senator Bernie Sanders that could ultimately be used to curtail military assistance. It is far from clear whether Sanders has the support to pass the resolution, but its introduction in the Senate this week – by an important progressive ally of the US president, Joe Biden – highlights mounting human rights and political concerns by Democrats on Capitol Hill. Citing the killing of nearly 19,000 people and wounding of more than 50,000 in Gaza since Hamas’s brutal 7 October attack, Sanders said it was time to force a debate on the bombing that has been carried out by the rightwing government of the Israel prime minister, Benjamin Netanyahu, and the US government’s “complicity” in the war. “This is a humanitarian cataclysm, and it is being done with American bombs and money. We need to face up to that fact – and then we need to end our complicity in those actions,” Sanders said in a statement. If passed, the resolution would force the US state department to report back to Congress any violations of internationally recognized human rights caused by “indiscriminate or disproportionate” military operations in Gaza, as well as “the blanket denial of basic humanitarian needs”. The state department would also have to report back on any actions the US has taken to limit civilian risk caused by Israeli actions, a summary of arms provided to Israel since 7 October, an assessment of Israel’s compliance with international humanitarian law in Gaza, and a certification that Israeli security forces have not committed any human rights violations. “We all know Hamas’s brutal terrorist attack began this war,” Sanders said. “But the Netanyahu government’s indiscriminate bombing is immoral, it is in violation of international law, and the Congress must demand answers about the conduct of this campaign. A just cause for war does not excuse atrocities in the conduct of that war.” Any such resolution would have to clear the Senate but only require a simple majority. It would also have to pass the House and be signed by the White House. The resolution includes details about the extensive use of US arms, including massive explosive ordinance, such as Mark 84 2,000lb bombs and 155mm artillery, and includes “credible findings” by human rights monitors and press organizations about the use of US arms in specific strikes that killed a large number of civilians. If the resolution were to pass, the administration would have 30 days to produce the requested report. After it is received, Congress would under US law be able to condition, restrict, terminate or continue security assistance to Israel. Congress has not requested such a resolution since 1976. Sanders has come under pressure from progressive Democrats to support calls for a ceasefire. Instead, the senator has previously called for a “humanitarian pause” to allow more aid into Gaza. In a letter to Biden this week, Sanders called on the US president to withdraw his support for a $10.1bn weapons package for Israel, which is contained in a proposed supplemental foreign aid package, and for the US to support a UN resolution it has previous vetoed demanding an immediate humanitarian ceasefire.