Iran's foreign ministry on Tuesday denied its Russian-built Bushehr nuclear power plant had suffered a malfunction, saying the process of its start-up was going ahead without a hitch.

"No problem has been reported at the Bushehr plant. The Russian contractors are overseeing the ongoing and normal process there," ministry spokesman Abbas Araqchi said in remarks reported by Iranian media.

His remarks came after Iran's ambassador to Moscow, Mahmoud Reza Sadjadi, said on Monday the plant had suffered a malfunction in its main generator, without giving further details.

Sadjadi said that Russian and Iranian specialists had been working "in close cooperation" to fix the malfunction.

He also stressed that the series of earthquakes that shook Iran in recent months had not caused the fault.

Reacting to those comments, Araqchi said Sadjadi may have been misquoted.

"Perhaps his remarks were not correctly reported, or were misinterpreted," Araqchi said.

"Before reaching its maximum capacity, we need to test the plant against all standards and this requires turning it off and on several times to ensure the safety of all equipment there," he added.

Iran's only nuclear power plant in Bushehr, located in the south off the Gulf, was officially inaugurated in September 2011 after years of construction delays.

But since then, the site has faced persistent technical problems, and has failed to reach its full production capacity of 1,000 megawatts.

Iran is the only country in the world with an operational nuclear reactor that does not adhere to the post-Chernobyl Convention on Nuclear Safety.

The country is also under rounds of United Nations Security Council sanctions for its refusal to stop enriching uranium that could be used to make weapons.

The Islamic republic, however, insists its atomic ambitions are limited to peaceful power generation and medical purposes only.