Former Central Intelligence Agency (CIA) director John Brennan has said he is “aware of information and intelligence” that revealed alleged contact between Russia and “US persons” in Donald Trump's campaign team.

Mr Brennan served as CIA director during Barack Obama’s second term in office and told the House of Representatives intelligence committee that he felt the investigation into alleged ties between the Trump campaign and Russia were “well founded.”

“I don’t know whether or not such collusion existed, but I know there was a basis of information for [an investigation],” said Mr Brennan referring to classified information he saw regarding alleged links between the Trump campaign and Russia.

“It raised questions in my mind about whether Russia was able to gain the cooperation of those individuals,” he said, adding that he did not know whether the Russian efforts were successful.

He added, “I don’t know whether such collusion existed.”

Republican Representative Trey Gowdy repeatedly pushed Mr Brennan to answer who exactly in the Trump campaign could have been involved with Moscow, but Mr Brennan was steadfast.

“I know there was a basis to have individuals to pull those threads” for further investigation, said Mr Brennan, adding that he would not identify anyone by name because the hearing was a public session.

He was scheduled to testify in a closed-door session with the House Committee after his public testimony.

But Mr Brennan did say that he had personally warned Russia last summer against interfering in the US presidential campaign, saying that continued meddling would backfire and prevent any warming of relations after the election.

Mr Brennan testified that he spoke with the head of the Russian intelligence service on 4 August 2016 and was the first US official to call out the Russians for their activities. He said the head of the FSB denied that Russia was meddling, but said he would raise the issue with President Vladimir Putin.

The former CIA chief also told the House Committee that he had become so concerned about Russian interference — and contacts between Americans “involved” with the Trump campaign and the Russians — that he convened a group of officials from the CIA, FBI and National Security Agency in late July to focus exclusively on the issue.

Mr Brennan explained several times that “it’s not CIA’s job” to investigate or assess the legality of actions of US persons.

“It’s our job to provide the [FBI] with all that information” so that they can investigate the situation further.

He confirmed that all relevant information gathered by the CIA was shared with former FBI Director James Comey.

Mr Brennan said that he has an “unfortunately grudging respect for Russian intelligence capabilities.” He said one of the tactics of the Russian intelligence agency is to “recruit” people in the US to further their agenda, whether that person is aware of their role or not.

“Russian intelligence agencies do not hesitate at all to use private companies...people not associated with government to further their agenda,” he said.

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Mr Brennan explained that Russian intelligence agencies also like to “recruit” businessmen and “rising politicians” in the US and other foreign countries to indirectly have an influence on that government and to advance Russian oligarchies interests - many of whom back Mr Putin.

Mr Putin and Russian intelligence services “are doing what they can to influence and undermine...in an underhanded, illegal way” the operations of western democracies, said Mr Brennan.

Some members of the committee questioned why Russia would be interested in Mr Trump winning but not Hillary Clinton.

Mr Brennan echoed a sentiment already expressed by Ms Clinton at a women’s conference earlier this month when she explained that Mr Putin blamed her for civil unrest after the last Russian election.

Ms Clinton said that in her former position as Secretary of State speaking out against undemocratic practises “kind of goes with the territory, at least it did prior to this administration.”

“I wasn’t telling...Russians something they didn’t know. So, they go out into streets in Moscow and St. Petersburg to demonstrate and Putin blames me,” Ms Clinton explained.

Mr Trump was “an outsider” and the Russians have a history of good relationships with businessmen, Mr Brennan explained.

They also felt Mr Trump would be more amenable to easing sanctions around the world that are not in the Russian interest.

The White House responded to Mr Brennan's testimony and said in a statement that "despite a year of investigation, there is still no evidence of any Russia-Trump campaign collusion." Their focus appears to be more on tracking down the "culprits" who leaked the information to the media.

“They anticipated that [Ms Clinton] was going to win the election. Efforts to denigrate her and hurt her would have continued into her presidency,” he said.

Mr Brennan said that none of the chaos and subsequent investigations in the US over the Russia election tampering scandal would likely deter them.