Hundreds of leaked Iranian intelligence documents have revealed Tehran's massive influence in Iraq, including paying Iraqi agents in the US to switch sides.

The unprecedented leak of 700 pages of the intelligence cables written mainly in 2014 and 2015 by Iran's Ministry of Intelligence and Security shows how Iran 'aggressively embedded' itself in its neighbouring country.

The reports obtained by the New York Times and the Intercept show how Iran is trying to infiltrate every aspect of Iraq's political, economic and religious life.

A poster of Iraq Parliament Speaker Mohammed al-Halbousi, right, and Iran President Hassan Rouhani, left, hang on a building near Tahrir Square, during ongoing protests in Baghdad

The secret source, who had declined to meet with a reporter in person, had said they wanted to 'let the world know what Iran is doing in my country Iraq'.

Among the revelations was how Iran had recruited former CIA informants after the United States pulled out its troops in 2011, leaving the assets 'jobless and destitute' and ready to share their knowledge.

And in one meeting between military intelligence officers from both countries, the Iraqi side had reportedly signalled to Iran: 'All of the Iraqi Army's intelligence - consider it yours.

Iraq has had close but complex ties with its large eastern neighbour, whose sway among Iraqi political and military actors grew vastly after the US-led invasion of 2003.

The new reports served to confirm the sentiment of protesters across Baghdad and the Shiite-majority south who oppose the current government and its backers in Iran.

'Iran is intervening in our country,' one demonstrator told AFP. 'But we, the people, are the decision makers.'

The demonstrator, a veiled Iraqi woman in her sixties, also greeted the fact that Iran had been hit by its own wave of protests since Friday, triggered by a sharp rise in petrol prices.

General Qasem Soleimani is Tehran's point man on Iraq

'The spark that started in Iraq has reached Iran,' she said.

The documents 'offer a detailed portrait of just how aggressively Tehran has worked to embed itself into Iraqi affairs, and of the unique role of General (Qasem) Soleimani,' wrote the outlets.

Soleimani, the head of the Iranian Revolutionary Guard Corps' elite Quds Force, is Tehran's point man on Iraq and travels there frequently during times of political turmoil.

Amid Iraq's largest and deadliest protests in decades, Soleimani has chaired meetings in Baghdad and Najaf in recent weeks to persuade political parties to close rank around Iraqi premier Adel Abdel Mahdi, sources have told AFP.

In one of the Iranian leaks, Abdel Mahdi is described as having had a 'special relationship' with Tehran when he was Iraq's oil minister in 2014.

The prime minister's office told AFP it had 'no comment' for the time being on the report.

The reports reveal how informants lurk at Baghdad airport, snapping pictures of American soldiers and keeping tabs on coalition military flights, sources are plied with gifts and Iraqi officials are offered bribes.

But other cables show serious ineptitude such as one which describes how Iranian spies broke into a German cultural institute in Iraq only to find they had the wrong codes and could not unlock the safes.

In one of the Iranian leaks, Prime Minister Adel Abdel Mahdi (pictured) is described as having had a 'special relationship' with Tehran when he was Iraq's oil minister in 2014

The reports also named former prime ministers Haider al-Abadi and Ibrahim al-Jafari as well as former speaker of parliament Salim al-Jabouri as politicians with close Iran links.

According to the NYT, Tehran was able to gain much more access following the withdrawal of US troops from Iraq in 2011, which it said left Iraqi assets of the Central Intelligence Agency 'jobless and destitute'.

The US invasion in 2003 left a vacuum in Iraq which was filled by Iranian power.

They then turned to Iran, offering information on the CIA's operations in Iraq in exchange for money, the report said.

In one incident, an Iraqi military intelligence officer had travelled from Baghdad to meet with an Iranian intelligence official in Iraq's holy city of Karbala.

During the three-hour meeting, the Iraqi official said his boss, Lieutenant General Hatem al-Maksusi, had told him to pass on the message to Iran that 'all of the Iraqi Army's intelligence - consider it yours'.

Al-Maksusi had also offered to give Iran information about a covert system established by the US to eavesdrop on Iraqi phones, run by the premier's office and military intelligence, the reports said.

Iran and Iraq fought a devastating war from 1980 to 1988 and were ferocious foes under dictator Saddam Hussein.

Many Iraqi dissidents under the Saddam regime sheltered in Iran but returned to political life in Baghdad following the brutal ruler's ouster in 2003.

Iran has therefore enjoyed close ties with the new generation of Iraqi politicians and has helped train military actors including in the Hashed al-Shaabi paramilitary network.

It is also a major trading partner, selling crucial electricity and natural gas to supplement Iraq's gutted power sector as well as goods ranging from fruit to carpets and cars.

Iran has used wide-ranging intelligence operations to maintain that deep influence, the NYT and The Intercept reported.

Its major goals were to 'keep Iraq from falling apart and prevent the emergence of an independent Kurdistan, among other strategic aims'.

The 'greater focus,' the NYT report said, was 'on maintaining Iraq as a client state of Iran and making sure that political factions loyal to Tehran remain in power'.