Israel says an Iranian-born man accused of spying for Iran's powerful Revolutionary Guards has been caught with photos of the United States embassy in Tel Aviv.

Israel's Shin Bet security service says 55-year-old Ali Mansouri was recruited as a spy last year by Iran's Quds Force, a paramilitary arm of the elite Revolutionary Guard.

The group is accused of running covert Iranian military operations abroad, as well as plotting terrorist attacks.

The agency says Mansouri confessed to being offered $US1 million to use his international business activities as a cover for his spying.

As well as photographs of the US embassy in Tel Aviv, Mansouri had shots of the inside of Israel's international airport, where he was ultimately arrested, Israel says.

He has also allegedly provided Israeli intelligence with the name of several Quds Force contacts, including his handler.

However, Mansouri's state-funded lawyers say he was denied legal advice for nine days.

Netanyahu aims to expose Iranian 'sweet talk'

News of Mansouri's arrest was released just hours after Israeli prime minister Benjamin Netanyahu left for the US, determined to expose what he described as "sweet talk" by Israel's arch-foe Iran.

Shin Bet says Mansouri had enrolled in a "special operations unit of the Revolutionary Guards responsible for numerous terrorist attacks around the world".

He has been using a Belgian passport and the fake identity Alex Mans, the agency says.

An Iranian national, he married a Belgian woman in 2006 but had since divorced, it says.

The Belga news agency quoted Belgian foreign minister Didier Reynders as saying that there was nothing to indicate the suspect had acquired Belgian nationality in an irregular manner.

Under questioning, he said he had been promised $US1 million to "harm Israeli and Western interests" on behalf of the Iranian intelligence services, and named four senior Iranian officials as alleged handlers.

He had previously visited Israel in July 2012 and last January.

On the diplomatic front, Mr Netanyahu has been dismissive in his response to the drive by Iran's new president Hassan Rouhani to mend fences with the international community, which culminated in an historic 15-minute telephone conversation with US president Barack Obama on Friday.

Israel, the Middle East's sole if undeclared nuclear-armed power, remains adamant that Iran is bent on developing a nuclear weapons capability, something it regards as a threat to its existence.

Israeli leaders have repeatedly vowed to take military action rather than see Iran develop a bomb, and have called on its US ally to take tougher action against Tehran, saying they see no real change of policy under Mr Rouhani.