The initiative was opposed by 52 senators and supported by 47 senators.
The vote marks the fourth time this year lawmakers have effectively allowed the US-Israeli war of aggression against Iran to continue without formal approval, despite concerns raised over its legality and scope.
Some senators acknowledged the need for a clear strategy, noting that under US law Congress must authorize military action within 60 days, a deadline approaching later this month.
At the same time, lawmakers warned that prolonging the conflict could lead to additional costs and instability, with discussions already turning to potential funding requests worth hundreds of billions of dollars.
On February 28, the United States and Israel launched strikes on targets in Iran, including in Tehran, causing damage and civilian casualties. Iran responded by striking Israeli territory and US military facilities in the Middle East.
On April 7, Washington and Tehran announced a two-week ceasefire. Subsequent talks in Islamabad ended without result. While no resumption of hostilities was announced, the US began a blockade of Iranian ports. Mediators are attempting to organize a new round of talks.