BEIRUT (Reuters) - Iran has begun work on infrastructure to build advanced centrifuges at its Natanz facility but will adhere to its 2015 nuclear deal with world powers, the director of Iran’s Atomic Energy Organisation Ali Akbar Salehi said on Tuesday.

On Monday Iran's Supreme Leader said he had ordered preparations to increase uranium enrichment capacity if the nuclear deal falls apart after the U.S. withdrawal from it in May.

According to a spokesman for Iran's nuclear agency, Tehran will inform the U.N. nuclear watchdog in Vienna on Tuesday that it had started the process to increase uranium enrichment capacity. [nL5N1T668E]

The decision by the United States to withdraw from the nuclear agreement has cast doubt on whether the remaining signatories will be able to preserve the deal.

The developing of infrastructure for building advanced centrifuges at the Natanz facility is moving along quickly, Salehi said in a news conference broadcast on state television.

"If we were progressing normally, it would have taken six or seven years, but this will now be ready in the coming weeks and months," Salehi said.

Iran has also developed the capacity to produce electricity at Natanz, Salehi said, a site which lies around 300 kilometers (186 miles) south of Tehran.

Salehi said none of Iran's nuclear activities would violate Tehran's landmark deal with world powers, under which it strictly limited uranium enrichment capacity to satisfy the powers that it could not be used to develop atomic bombs.

In exchange, Iran received relief from sanctions, most of which were rescinded in January 2016.

The deal allows Iran to continue 3.67 percent uranium enrichment, far below the roughly 90 percent threshold of weapons-grade. Before the deal was reached, Tehran enriched uranium to up to 20 percent purity.