U.S. President Barack Obama on Tuesday showered praise on Hillary Clinton's judgement and toughness hours after FBI Director James Comey blasted the presumptive Democratic presidential nominee for being "extremely careless" in handling classified information.

"I'm here today because I believe in Hillary Clinton," said Obama during his 2016 debut on the campaign trail at a rally in Charlotte, North Carolina. "There has never been a man or woman more qualified for this office than Hillary Clinton. Ever. And that's the truth."

Speaking to a roaring crowd of Clinton supporters, Obama reminded them and TV viewers across the country of his bitter experience of competing against the strong-minded former first lady in the 2008 primary season and of Clinton's "grace and the energy with which she threw herself into my campaign."

"I came away from that primary admiring her even more, because during that year and a half, I had a chance to see up close just how smart she was and just how prepared she was," said Obama who hailed Hillary in first joint campaign appearance.

While slamming Donald Trump, the presumptive Republican nominee, for his "tough talk" and "phony bluster", Obama lauded Clinton's past record as his top diplomat as evidence of her exceptional judgement and toughness.

"My faith in Hillary Clinton has always been rewarded. I have had a front-row seat to her judgement and her toughness and her commitment to diplomacy. And I witnessed it in the Situation Room where she argued in favor of the mission to get Bin Laden," said Obama.

Obama's praise of Clinton's judgement came just hours after FBI chief Comey criticized her for her private email setup during her stint at the State Department, describing her and her senior aides as being "extremely careless" in handling sensitive information.

Comey said federal investigators found that 110 emails in 52 email chains had contained classified information at the time they were sent or received and that eight of those 52 chains "contained information that was top secret" when they were sent.

Apart from the approximately 30,000 work-related emails Clinton turned over to the State Department in 2014, investigators later discovered several thousand work-related e-mails that were not among the group of 30,000 e-mails, Comey told a press conference in Washington, D.C.

"With respect to the thousands of e-mails we found that were not among those produced to the State Department, agencies have concluded that three of those were classified at the time they were sent or received; one at the secret level and two at the confidential level," he said.

However, the FBI would not recommend criminal charges against Clinton for her use of a private email server as secretary of state, said Comey, adding that here was no clear evidence that Clinton and her aides intended to violate the law.

The FBI's recommendation on Tuesday immediately drew criticism from Republicans, with House Speaker Paul Ryan questioning whether "damage is being done to the rule of law" in the case.

"No one should be above the law," said Ryan in a statement. "Declining to prosecute Secretary Clinton for recklessly mishandling and transmitting national security information will set a terrible precedent."

Meanwhile, Republican National Committee Chairman Reince Priebus on Tuesday said in a statement that the FBI decision was rigged.

"This is grossly negligent conduct on the part of Hillary Clinton and her aides, but as the Obama Administration has repeatedly shown throughout this process, they were never going to prosecute Clinton's criminal behavior because they are counting on her to deliver their failed agenda a third term," said the statement.

Comey has in the first place defended the FBI investigation as being done "honestly, competently and independently."

"I know there were many opinions from people who were not part of the investigation, including people in government. But none of that mattered to us," said Comey. "No outside influences of any kind was brought to bear."

Early this year, U.S. President Barack Obama weighed in on Clinton's intent of using a private email setup during her stint at the State Department.

He told Fox News in an interview that he believed that Clinton did not intentionally endanger national security in her handling of classified information.

The remarks immediately raised concerns that the federal investigators could be swayed by the president's view on the issue.

The FBI announcement also came a week after former U.S. President Bill Clinton had a private meeting with Attorney General Loretta Lynch.

The 30-minute meeting on June 27 at the Phoenix International Airport in Arizona, which Lynch described as primarily social, raised concerns about a potential conflict of interests.

According to ABC News who first disclosed the meeting, Mr. Clinton waited for Lynch's arrival after being notified that she would be arriving at the same airport. Mr. Clinton approached Lynch and initiated the unplanned chat.

Speaking on Friday at Aspen Ideas Festival in Aspen, Colorado, Lynch indicated her regrets about not having turned down the former president.

She also announced that she "fully" expected herself to accept recommendation by FBI investigators on whether to bring charges related to Hillary Clinton's personal email setup.

Lynch said her decision to accept FBI recommendation was made long before her impromptu chat with Mr. Clinton.
Source:XINHUA