UNITED NATIONS  The United Nations Security Council leveled its fourth round of sanctions against Iran’s nuclear program on Wednesday, but the measures did little to overcome widespread doubts that they  or even the additional steps pledged by American and European officials  would accomplish the Council’s longstanding goal: halting Iran’s production of nuclear fuel.

The new resolution, hailed by President Obama as delivering “the toughest sanctions ever faced by the Iranian government,” took months to negotiate and major concessions by American officials, but still failed to carry the symbolic weight of a unanimous decision. Twelve of the 15 nations on the Council voted for the measure, while Turkey and Brazil voted against it and Lebanon abstained.

The United States and Europe acknowledged before negotiations started that they would not get the tough sanctions they were hoping for, promising to enact harsher measures on their own once they had the imprimatur of the United Nations. Congress is expected to pass a package of unilateral sanctions against Iran, and European leaders will begin discussing possible measures at a summit meeting next week.

“We would want to have a tough translation of the resolution,” said Gérard Araud, the French envoy to the United Nations.