And "the process of getting consensus" in the UN Security Council is "always challenging," cautioned Undersecretary of State for Political Affairs William Burns said in a prepared statement to the Senate Armed Services Committee.
Faced with Iran's defiance of world pressure to freeze its suspect nuclear program, "we are moving with a sense of urgency toward a new UN Security Council resolution," Burns said.
"We are working aggressively to adopt concrete measures that will serve as a platform to strengthen and expand upon existing sanctions and target the power centers mostly likely to have an impact on Iran's strategic calculus," he said.
Burns, who spoke as legislation imposing new unilateral US sanctions against Iran seemed stalled, noted that Iran was also facing pressure from decisions by some long-standing trade and investment partners to end their relationships.
"Neither our formal penalties nor the increasing ostracism Iran faces from the world will alter its agenda overnight, but we believe that the mounting weight of political and financial pressures on its leadership can persuade Tehran to reassess its approach to the world," said Burns.
The US Senate and House of Representatives have passed rival versions of legislation imposing a set of US sanctions on Iran, but have yet to name lawmakers to a "conference" to thrash out a compromise version to send to President Barack Obama.
Lawmakers have ramped up calls for Washington to target Iran's imports of gasoline and other refined petroleum products.
Because of a lack of domestic refining capacity, oil-rich Iran is dependent on gasoline imports to meet about 40 percent of domestic consumption.
Iran denies Western charges that its atomic program hides a quest for nuclear weapons, and is under several rounds of UN sanctions for refusing to halt uranium enrichment.
