The US Army ordered the illegal use of psychological operations to influence US politicians on the Afghanistan war, Rolling Stone magazine reported, forcing the US commander there to launch an inquiry.

The explosive article said the command of General William Caldwell, in charge of training Afghan troops, pressured US soldiers specialising in "psy-ops" to manipulate visiting US senators and congressmen - as well as other VIPs and senior foreign officials - into supporting more money and troops for the war.

The report shook Washington at a time of growing public dissatisfaction with the longest US war, with lawmakers urging a swift investigation of the "disturbing" charges.

Pentagon spokesman Colonel David Lapan said war commander General David Petraeus "is preparing to order an investigation" to determine "what actions took place and if any of them was inappropriate or illegal".

Defence secretary Robert Gates "is aware of the allegations" in the article, and "fully supports General Petraeus's decision to investigate this matter before drawing any conclusions," said Pentagon spokesman Geoffrey Morrell.

The report says an army lieutenant colonel told the magazine he had been repeatedly ordered by General Caldwell's staff to target senators, including 2008 Republican presidential nominee John McCain, Joe Lieberman, Jack Reed, Al Franken and Carl Levin.

Among those the team was told to pressure during a four-month period were chairman of the Joint Chiefs of Staff Admiral Mike Mullen, Germany's interior minister, and the Czech ambassador to Kabul, according to members of the "information operations" (IO) team and internal documents.

And when the officer sought to bring the operation to a halt, a campaign of retaliation was launched against him, according to the magazine.

"My job in psy-ops is to play with people's heads, to get the enemy to behave the way we want them to behave," Lieutenant Colonel Michael Holmes, leader of the IO unit, told Rolling Stone.

"I'm prohibited from doing that to our own people. When you ask me to try to use these skills on senators and congressman, you're crossing a line."

The magazine also said General Caldwell's chief of staff asked Lt Col Holmes how the general could secretly manipulate the US lawmakers.

"How do we get these guys to give us more people?" the chief of staff demanded. "What do I have to plant inside their heads?"

Investigation

An inquiry will likely check whether the IO effort was in violation of US law that forbids targeting US nationals with such propaganda campaigns.

These are "serious charges that must and will be fully investigated," said Mr Reed, a Democrat who sits on key committees with oversight over the conflict.

Both Mr Reed and Mr Levin, the Senate Armed Services Committee chairman, denied they had been influenced by the effort.

Mr Reed said in a statement that on each of the 11 trips he has made to Afghanistan since the war began he tries "to cast a wide net and gather information from many sources".

The report was the second dramatic scoop on military issues by the iconic music magazine in less than a year.

In 2010, Michael Hastings, the same writer, wrote a withering critique of General Petraeus's predecessor, General Stanley McChrystal, and his staff, attributing blunt comments to the commander's staff in an article which led to General McChrystal's sacking.

Hastings wrote that Lt Col Holmes - who became the subject of an army investigation after emailing a military lawyer to address his discomfort with the psy-op orders on US civilians - said General Caldwell "seemed far more focused on the Americans and the funding stream than he was on the Afghans".

"We were there to teach and train the Afghans. But for the first four months it was all about the US," he added. "Later he even started talking about targeting the NATO populations."

In response to Lt Col Holmes's email, military lawyer Captain John Scott agreed with Lt Col Holmes and wrote "IO doesn't do that", according to the report.

"(Public affairs) works on the hearts and minds of our own citizens and IO works on the hearts and minds of the citizens of other nations," Captain Scott wrote.

"While the twain do occasionally intersect, such intersections ... should be unintentional."

In a statement to the magazine, a spokesman for General Caldwell "categorically denies the assertion that the command used an Information Operations Cell to influence distinguished visitors".

- AFP