The United States decided not to reimpose sanctions on Iran's nuclear program Wednesday despite President Donald Trump's criticism of the deal Tehran signed with the previous US administration.

But, while the waiver on the nuclear-related sanctions was renewed, the US Treasury imposed new measures to punish Iranian defense officials and a Chinese business tied to Tehran's missile program.

The decision not to renew sanctions came just two days before Iran is due to go to the polls and may prove a boost for President Hassan Rouhani, who signed the deal and is seeking re-election.

Under the terms of the 2015 deal, the previous US administration of president Barack Obama agreed to waive sanctions on Iran's nuclear program in return for strict controls to prevent its developing a nuclear bomb.

Some of those waivers come up for review this week, for the first time since Trump was elected after warning during his presidential campaign that he might rip up the agreement.

But Washington's top diplomat for the Middle East, Stuart Jones, said in a statement that the department had told Congress that “the United States continues to waive sanctions” that were lifted under the Iran deal.

Nevertheless, he added, the Treasury will apply new targeted sanctions on individuals and firms helping Iran's banned ballistic missile program and to hold Tehran to account for rights abuses.

“Iran continues to pursue missile-related technologies capable of delivering a nuclear weapon,” he said, noting that the missile program is in breach of internationally-backed UN Security Council resolutions.

“The State Department will continue to partner with our colleagues at the Department of the Treasury to ensure our national security in the face of Iranian threats. “