US President Barack Obama should be investigated because he "knew all about" Hillary Clinton’s email arrangements, Republican presidential candidate Donald Trump said.

"That's why he stuck up for Hillary, because he didn't want to be dragged in. Because he knew all about her private server," Trump said in an interview with Reuters. "This means that he has to be investigated."

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On Tuesday, WikiLeaks published another batch of emails from the private account of Clinton's campaign chairman, John Podesta. One of the emailed exchanges showed the campaign reacting to Obama that he learned of Clinton’s private email server use from the news.

"We need to clean this up – he has emails from her – they do not say state.gov," Cheryl Mills, a longtime Clinton aide, wrote to Podesta after Obama made the comments in a March 2015 television interview.

Following Obama’s comments to CBS News in March 2015, White House spokesman Josh Earnest walked back the presidential statement, saying that the two “did have the occasion to email each other.”

READ MORE: #Podesta conspiracy 2.0: Ex-Swedish PM & Soros ally Bildt makes false RT-WikiLeaks claims

However, he insisted that Obama “was not aware” of the details of Clinton’s email account, but added that the president “recognized the email address that he was emailing back to.”

In his interview at the time, Obama also said that he believed Clinton’s emails and use of her private server “posed a national security problem."

After losing the 2008 Democratic primary race, Clinton served as Obama’s secretary of state between 2009 and 2013.During that time, she used a private email server to communicate with her aides, the State Department staff, and even the White House, as previous WikiLeaks disclosures showed.

According to the State Department, there were at least 18 emails exchanged between Obama and Clinton when she was secretary of state that were found on her home-brew server in Chappaqua. None of those, however, would be released because of a law that protects presidential communications from becoming public for several years.

The State Department was ordered to release all 55,000 pages of Clinton's emails between May 2015 and January 2016. More than 2,000 of the emails appeared to have classified information and were labeled as “confidential” and “secret.”

‘Top secret’ info on 22 Clinton emails means they won’t be released - State Dept. https://t.co/bco6Hks7hwpic.twitter.com/yxQCdJAEKU — RT America (@RT_America) January 30, 2016

On top of that, the FBI has also provided the State Department with about 14,900 work-related emails that were not in Clinton’s initial disclosure. Last Friday, the department released a batch of those emails, which were mostly redacted. The next releases are scheduled for November 3 and 4.

Already targeted by the scandal, Clinton’s campaign has also been struck by revelations made by WikiLeaks and hackers. Over the last week and a half, WikiLeaks has released 18 batches of the so-called “Podesta emails,” exposing communications between her campaign chair John Podesta and staff.