WASHINGTON : The United States plans to keep up its sanctions regime against Iran, even as it seeks a diplomatic solution over Tehran’s suspect nuclear program, a senior US official said Thursday.

International sanctions over what the West says is a nuclear weapons program have badly hit Iran’s economy and its leaders have made it clear they are looking for relief. “We have been clear that only concrete and verifiable steps can offer a path to sanctions relief,” Undersecretary of State for Political Affairs Wendy Sherman told lawmakers.

“Let me assure you that we will continue to vigorously enforce the sanctions that are in place as we explore a negotiated resolution, and will be especially focused on sanctions evasion and efforts by the Iranians to relieve the pressure.”

But Sherman, speaking to the Senate Foreign Relations Committee, warned that the political crisis gripping Washington was hampering its ability to enforce the punitive measures.

“Our ability to do that, to enforce sanctions, to stop sanction evaders, is being hampered significantly by the shutdown,” she said.

At midnight on Monday, the US federal government ran out of funding after a divided Congress failed to pass a stop-gap budget measure, sending hundreds of thousands of government workers homes and curtailing federal agencies’ work.

Sherman is leading the US delegation in talks between Western negotiators and Iranian representatives. A meeting is set to take place October 15-16 in Geneva, in a first test of recent overtures by Iran’s new President Hassan Rouhani.

During a visit to Tokyo earlier, Secretary of State John Kerry said the United States will not take Iran at its word over pledges of openness on its nuclear program, after Israel threatened to act against Tehran.

The major powers and Israel suspect Iran is seeking to develop nuclear weapons under the guise of a civilian energy program.