Investigations into the alleged manipulation of intelligence regarding the Islamic State and other terror groups have significantly expanded, with one whistle-blower meeting recently with congressional aides, Fox News has learned. 

A congressional source confirmed that aides on the Senate intelligence and armed services committees have met with the whistle-blower. 

At least five congressional committees -- including those two panels -- are now looking into the allegations. And Bloomberg reported Thursday that multiple inspectors general in the intelligence community have launched their own probes. 

The widespread involvement marks a significant expansion for a probe initially handled only by the Defense Department inspector general. Bloomberg reported that the whistle-blower who met with aides will meet with top senators soon. 

At their core, the allegations cover claims that Central Command figures manipulated analysts' intelligence to make the campaign against ISIS seem more successful. 

As Fox News previously reported, the alleged manipulation, though, predates even the rise of the Islamic State. 

Rep. Devin Nunes, R-Calif., chairman of the House intelligence committee, said these practices extend to how intelligence on Al Qaeda was handled as well. 

"I know for a fact this was going on in 2012, because I was told by informants that this was going on back then," Nunes, head of the intelligence committee, recently told Fox News. 

Nunes has said that in addition to the complaints that ISIS intelligence assessments hyped battlefield damage by the U.S. air campaign, there were significant complaints about the handling of the Usama bin Laden documents. 

The White House insisted last week that no one in the administration pressured anyone, and suggested blame may rest with the military. "The inspector general, I believe it's a Department of Defense inspector general, that's considering actions that may or may not have been taken by a range of officials inside the Department of Defense. I don't think there are any accusations that have been made against the White House officials," White House Press Secretary Josh Earnest said. 

The House oversight, armed services and intelligence committees also are looking into the allegations. 

Fox News' Catherine Herridge and Kara Rowland contributed to this report.