US lawmakers on Wednesday launched a bipartisan effort to end American involvement in Saudi Arabia's conflict with Yemen, an extraordinary attempt to force a vote on whether to over-rule presidential military authorization.
The United Nations has described Yemen, the poorest country in the Middle East, as the world's largest humanitarian disaster.
More than 9,200 people have been killed and tens of thousands wounded in Yemen's three-year-old war, which is seen as both a civil conflict and a proxy war between regional titans Saudi Arabia and Iran.
Since 2015 Washington has provided weapons, intelligence and aerial refueling for a Saudi-led coalition which has conducted air strikes against Huthi rebels.
Senators Bernie Sanders, Mike Lee and Chris Murphy said in a joint statement that their resolution would force the first-ever vote in the Senate "to withdraw US armed forces from an unauthorized war."
President Donald Trump's top military and diplomatic advisors said last October that the administration was not seeking new authority for conducting military operations in the world's hot spots.
Congress first passed an authorization to use military force, or AUMF, on September 14, 2001 -- three days after the devastating attacks on New York and Washington by Al-Qaeda hijackers.
Since then, presidents George W Bush, Barack Obama and now Trump have relied on the order's authority, along with a subsequent AUMF in 2002, as they launched operations against armed Islamist groups in far-flung battle zones around the world.
Several Democrats, and some Republicans, have warned that the 15-year-old authorities are licenses for endless US military engagement.