WASHINGTON — Sen. Angus King, I-Maine, warned Tuesday that congressional passage of new sanctions against Iran could scuttle international negotiations and cause the U.S. to miss “a once-in-a-generation opportunity” to prevent a nuclear-armed Iranian regime without conflict.

“These moments come and go in history but we have got to seize this one,” King said. “Not naively or blindly . . . but realistically with our eyes open and understanding the risks and understanding the importance of verification.”

King made his remarks at a Council on Foreign Relations event at a time when some on Capitol Hill continue to push for additional economic sanctions on Iran despite an interim agreement between the White House, the Iranians and an international coalition that aims to slow Iran’s development of nuclear weapons.

A Senate sanctions bill has nearly 60 sponsors from both sides of the political aisle despite strong objections from the White House. But on Tuesday morning, the Reuters news agency reported that the bill’s backers were no longer pushing to bring the bill to the Senate floor for discussion and were, instead, discussing a non-binding resolution.

King, who serves on both the Senate Intelligence Committee and the Senate Armed Services Committee, said he believes Congress’ threat of new sanctions has kept pressure on Iran. Congress plays an important role as “the sword in the sheath . . . but you don’t have to bear the sword.”

Passage of additional sanctions could prompt Iran to walk away from the negotiating table and undermine the international coalition, he said.

“I see very little upside to passing a bill of this nature now,” King told several dozen people at the Council on Foreign Relations, a nonpartisan foreign policy organization. “It may strengthen the president’s hand, maybe. That’s the possible upside. But the downside I view as enormous. If they walk, if the talks end, if the sanctions coalition falls apart we may have missed a once-in-a-generation opportunity to deal with this problem.”

Tuesday’s event was the second time in recent days when King spoke out publicly about new sanctions.

In an op-ed published Monday by The New York Times, King and Sen. Carl Levin, D-Mich. wrote that negotiations or military action are the only two routes to keeping the Iranian regime from developing nuclear weapons.

Levin, who chairs the Senate Armed Services Committee, and King wrote that moving forward with new sanctions “risks scuttling the process and could have damaging ramifications for the United States as well as our regional allies and partners, especially Israel.”

They warned that pushing forward with new sanctions could give hard-line elements in Iran a reason to walk away from negotiations while alienating “our international partners” who are trying to avert a nuclear-armed Iran.

“Instead of slowing Iran’s nuclear program, such legislation could actually accelerate its quest for atomic weapons, leaving a stark choice: Either accept the possibility of a nuclear-armed Iran, or use military force to stop it,” reads the op-ed.