Washington - CIA contractors likely breached security and handed over documents about the agency's use of hacking tools to anti-secrecy group WikiLeaks, US intelligence and law enforcement officials told Reuters on Wednesday.

Two officials speaking on condition of anonymity said intelligence agencies have been aware since the end of last year of the breach, which led to WikiLeaks releasing thousands of pages on Tuesday.

According to the documents, Central Intelligence Agency hackers could get into Apple iPhones, devices running Google's Android software and other gadgets in order to capture text and voice messages before they were encrypted with sophisticated software.

The White House said on Wednesday that US President Donald Trump was "extremely concerned" about the CIA security breach that led to the WikiLeaks release.

"Anybody who leaks classified information will be held to the highest degree of law," spokesman Sean Spicer told reporters.

The two officials told Reuters they believed the published documents about CIA hacking techniques used between 2013 and 2016 were authentic.

One of the officials with knowledge of the investigation said companies that are contractors for the CIA have been checking to see which of their employees had access to the material that WikiLeaks published, and then going over their computer logs, emails and other communications for any evidence of who might be responsible.

On Tuesday in a press release, WikiLeaks itself said the CIA had "lost control" of an archive of hacking methods and it appeared to have been circulated "among former US government hackers and contractors in an unauthorized manner, one of whom has provided WikiLeaks with portions of the archive".

A US government source familiar with the matter said it would be normal for the Federal Bureau of Investigation and the CIA both to open investigations into such leaks. US officials previously have confirmed that prosecutors in Alexandria, Virginia for years have been conducting a federal grand jury investigation of WikiLeaks and its personnel.

A spokesman for the prosecutors declined to comment on the possibility of that probe being expanded. It is not clear if the investigation of the latest CIA leaks is part of the probe.

Apple, Alphabet Inc's Google, Cisco Systems Inc and Oracle Corp did not immediately respond when asked if they were notified of a CIA breach before WikiLeaks made its files public.