Masoud Barzani, the ex-president of the Kurdish Regional Government (KRG) in northern Iraq, has said that a major Iraqi operation last month to take over Kirkuk and other Kurdish-held areas took place with the full knowledge of the US and the UK.

The Iraqi army, backed by Shia militia, captured the entirety of the oil-rich Kirkuk province on October 21 after a rapid advance in the wake of a controversial referendum on Kurdish secession that Baghdad had declared illegal.

"We do believe, yes, that the operation to take over Kirkuk was led by Iranians with the knowledge of the US and British officials," Barzani, 71, said in an interview with Newsweek.

The referendum, which was held on September 25, received an overwhelming 93 percent approval, despite lacking regional and international support, including from the US.

Barzani, who quit his position from the KRG and president of his Kurdistan Democratic Party on November 1, defended the decision to go ahead with the vote.

"We believe the timing was good ... because those Iraqi forces who are currently implementing their policies to change the demography and situation in areas that they are in right now, they had this programme and this plan in mind even before the referendum," he said in the Newsweek interview.

"They are using the referendum as a pretext to cover their plan and plot against the Kurdish people.

"When asked if the KRG's relationship with Washington has changed since President Donald Trump took office in January, Barzani replied: "With regards to the relationship between Kurdistan and the White House ... I can't say whether we have a relationship or not."

'Big surprise for us'

Barzani also said without the contribution of the Kurdish Peshmerga forces, ISIL "would not have been rolled back and defeated" in Iraq, including in Mosul, the country's second-largest city.

"But we were not expecting to see Iraqi forces use weapons - that were given to them by the US to fight ISIS - against their own citizens," he said, using a different name for ISIL.

"It was a big surprise for us."

Sadi Pire, a senior KRG official and member of the Patriotic Union of Kurdistan party, told Al Jazeera that the US "definitely had knowledge" of the Iraqi forces' plan to enter Kirkuk.

"The US saw that the referendum would weaken the relationship between the [Kurdish] Peshmerga and the Iraqi forces, which would lead to clashes and a general weakening of forces fighting against terrorism," said Pire.

"The US favoured postponing the referendum because its main priority is the fight against Daesh," he added, using the Arabic acronym for ISIL.

"But it also made it clear that it would not fight against the Iraqi forces if they took over the Kirkuk province."

'Seeking dialogue'

The Peshmerga seized Kirkuk, Iraq's second oil hub, in mid-2014 when Iraqi troops withdrew from the advancing ISIL armed group.

But last month's operation by the Iraqi army resulted in Baghdad retaking five oil fields from the Kurdish forces.

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This dealt a heavy blow to the KRG's finances who had depended on revenues from exports of Kirkuk oil.

Yet Barzani, whose responsibilities have been distributed to the judiciary and parliament, said the Kurds do not seek an escalation of tensions with the federal government in Baghdad.

"Our policy is to seek dialogue, to seek peaceful ways for conflict resolution and conflict prevention with Iraq," he told Newsweek.

"We are ready to go as far as it's possible to avoid fighting with the Iraqi army, as long as they are not … changing the [autonomous] status of Kurdistan."