Federal intelligence agencies should examine at least 305 Clinton emails for sensitive information, US State Department said on Monday.

"It doesn't mean that all 300 are going to end up at some level of (classification upgrade). I suspect some will and I suspect some won't," State Department spokesman John Kirby told reporters.

The messages are a part of 1,500 documents analyzed so far by the State Department in the controversy surrounding former first lady and presidential candidate, Hillary Clinton.

'Top secret'

Clinton came under public scrutiny for using a private server for her emails while serving as Obama's secretary of state. The government forbids sending of classified information over unsecured network, and there is no evidence that she used encryption to shield the emails from foreign intelligence services or other prying eyes.

The US politician claims she exchanged around 62,000 messages between 2009 and 2013, with almost half the emails being official and the rest private.

At least two of her e-mails contained information deemed "top secret," according to a government watchdog who examined a sample of 40 messages.

However, Clinton has repeatedly denied using her private account to handle information that was classified at the time. She has also stated that the she only used her private account as a matter of convenience.

Half of the emails wiped

Clinton has handed over her official correspondence to the State Department, while deleting over 30,000 of personal emails from her home-based server.

Republicans accuse Clinton for lack of transparency, as the private server could make it easier to contravene the law requiring all written communication of government officials to be preserved.

Power struggle

The US State Department has released a total of 3,500 of Clinton documents since late May, and all of the information, except the documents redacted by the government agency or intelligence services, is set to be released by next January.

Dozens of the e-mails have been reclassified after the release, according to State Department representative Kirby.

"Most of these are at a very low level, what we call confidential," he added.

The controversy surrounding the emails could influence Hillary Clinton's 2016 presidential bid, possibly turning the tide against the Democratic front-runner.

dj/kms (AFP, Reuters, AP)