Iran used the UN General Assembly on Thursday to accuse the United States of failing to meet its commitments under a historic nuclear deal.

President Hassan Rouhani complained that America is dragging its feet on its side of the bargain.

"The lack of compliance (with the deal) on the part of the United States in the past several months represents a flawed approach that should be rectified forthwith," Rouhani told the world body.

The agreement between Tehran, Washington and five other major powers came into force in January. Iran accepted curbs to its nuclear program in exchange for their lifting sanctions.

While observers say Iran has met its commitments, Tehran accuses Washington of continuing to block the Islamic republic from the international banking system, limiting its ability to benefit from the lifting of sanctions.

Iran says the deal has already boosted its oil exports, but that international banks are concerned they may be prosecuted by the US Treasury if they do business with Iran.

"They scare, they frighten the big banks with the threat of potential action by the United States Treasury. This is something that we oppose," Rouhani told reporters following his address.

He accused the United States of causing delays, a "complete lack of transparency" and failure to take action on its commitments.

"Other nations are working hard to realise their commitments," he said.

- 'A victory' -

On returning to Iran on Friday, Rouhani told reporters that the United States had promised to comply with the deal.

The US made the pledge during a meeting of foreign ministers of world powers who signed the deal, he told reporters at Tehran airport.

"The US promised to correct the procedure," he said.

The other parties to the deal also told the US it was not complying, he said.

"This is very important in my opinion," he said. "It was a victory."

Tehran has threatened to take action in the International Court of Justice against the United States if $2 billion in frozen assets belonging to its central bank is diverted to American victims of terror attacks.

"We see this as an international heist to be quite frank," Rouhani told reporters in New York. "I am certain that we will be legally victorious and the United States will be fined for this transgression," he added.

But he also gave a staunch defense of the nuclear deal as in the best interests of Iran, its economy and its people, saying that trade with the European Union was up more than 44 percent already this month.

"The question then becomes what will we do if the United States continues non-adherence," he said, referring to complaint mechanisms built into the deal.

"A complaint would be brought to this joint commission and the ministers of foreign affairs from seven countries would talk," he said.

Asked about November's US presidential election, with Democrat Hillary Clinton competing against Republican Donald Trump, Rouhani said it made no difference to Iran who won as long as the incoming US administration respected Iran and decreased tension.

The nuclear agreement has faced opposition from ultra-conservatives in Iran and the United States, led by Republican opponents of Democratic President Barack Obama's administration.

Addressing reporters in Tehran on Friday, Rouhani said Iran was meeting its side of the deal.

"Of course, we ourselves, as always and as the supreme leader has stressed, meet our commitments according to our Islamic duties, as long as the other side meets its commitments," he said.