TEHRAN, Iran – The top foreign adviser to Iran's supreme leader on Friday called for separate talks directly with the United States amid the multilateral negotiations over Iran's nuclear program.

The remarks by Ali Akbar Velayati signaled a high-level endorsement of the policies of President Hassan Rowhani, who has been sharply criticized by hard-liners over the landmark nuclear deal that Iran reached with world powers last month and over other contacts with the U.S.

Velayati said Iran benefits by talking separately with each of the so-called 5+1 powers — the grouping of the United States, Russia, France, Britain, China and Germany, with which it negotiated the interim nuclear deal and with which it is still to work out a permanent accord. Each has separate interests, he said in comments on television.

"We aren't on the right path if we don't have one-on-one talks with the six countries," he said. "We have to talks with the countries separately. … It would be wrong if we bring the countries into unity against us, since there are rifts among them over various international issues."

Opposition from hard-liners

Hard-liners have blasted the nuclear accord as a surrender to Western pressure and criticized Rowhani over a phone conversation he had with President Obama in September.

U.S. officials have also said Iran and the Americans met in secret for months ahead of the nuclear deal. Under the accord, reached in Geneva, Iran is to limit its uranium enrichment for six months in return for an easing of some sanctions, pending a permanent deal.

Experts from Iran and the world powers will hold a new round of talks Monday in Geneva on implementing the interim accord.

The United States and its allies accuse Iran of seeking to build a nuclear weapon. Iran denies the charge saying its program is only for peaceful purposes, including power generation and developing medical treatments.

New centrifuges built

Iran's nuclear chief Ali Akbar Salehi said this week that the country is building a new generation of centrifuges for uranium enrichment but they need further tests before they can be mass produced.

His comments appeared aimed at countering hard-liner criticism by showing the nuclear program is moving ahead despite the accord.

"The new generation of centrifuges is under development. But all tests should be carried on it before mass production," Salehi said. He did not say how long that would take.

He also said Iran has a total of 19,000 centrifuges. In August, Iran said it had 18,000, including some 1,000 advanced ones. Iran previously gave the U.N. nuclear watchdog information on the new machines, which are able to enrich uranium faster.

Under the Geneva deal, Iran agreed to limit its uranium enrichment to 5 percent and neutralize its stockpile.

Uranium can be used to build a weapon if it is enriched more than 90 percent.