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 Friday by Ali Akbar Velayati signaled a high-level endorsement of the policies of President Hassan Rouhani, who has been been sharply criticized by hardliners 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 that were also carried on the semi-official Mehr news agency.

"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."

Hard-liners have blasted the nuclear accord as a surrender to Western pressure and have criticized Rouhani over phone conversation he had with President Barack Obama in September when Iranian Foreign Minister Mohammad Javad Zarif met with his American counterpart. 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 negotiation of 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, one of Iran's senior negotiators, Abbas Araghchi, and Maja Kocijancic, the spokeswoman for EU foreign policy chief Catherine Ashton said Friday.

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.

Iran's nuclear chief Ali Akbar Salehi said late Thursday 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 and has not been halted by the accord.

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

He also said Iran has a total of 19,000 centrifuges, though he did not say how many were operational. In August, Iran said it had 18,000 including some 1,000 advanced ones centrifuges. Iran previously gave the U.N. nuclear watchdog information on the new generation of 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 of 20-percent enriched uranium.

Enriched uranium can be used to build a weapon if it is enriched more than 90 percent. At lower levels, it is used to power nuclear reactors.