The move comes months after the company promised to crackdown on illegal practices in the wake of another emerging markets scandal that involved the company bribing doctors with cash and sexual favours in China.
GSK, which promised to "root out corruption wherever it exists" in the wake of the Chinese revelations, was on Monday forced to admit that it was "investigating allegations of improper conduct in our Iraq business".
The FTSE 100 company said it was urgently looking into whistleblower claims that it hired 16 Iraqi government doctors and pharmacists to act as sales representatives and improperly boost its sales.
Details of the allegations, which are said to have originated in 2012 but continue to this day, were sent to company executives by a whistleblower, according to the Wall Street Journal. The emails claim the alleged malpractice breaches the UK's Bribery Act and the US Foreign Corrupt Practices Act, which ban bribery of foreign officials.
A GSK spokesman said: "We have zero tolerance for unethical or illegal behaviour. We employ fewer than 60 people in Iraq in our pharmaceutical operation and these allegations relate to a small number of individuals in the country.
"However, we are investigating whether there have been any improper conduct and these investigations are ongoing."
The move comes as the Chinese authorities continue to investigate allegations that some senior GSK Chinese executives broke the law in a £320m cash and sexual favours bribery scandal.
GSK's chief executive, Sir Andrew Witty, has described the Chinese allegations as shameful and said: "To be crystal clear, we have zero tolerance to this sort of behaviour."
Witty, who was paid £6.5m last year, had promised to root out corruption and said the company would stop paying doctors to promote drugs.
Witty dispatched Abbas Hussain, the drugmaker's head of emerging markets, to Shanghai last year to apologise to the Chinese authorities for the scandal and promised the company was taking the charges extremely seriously.
Hussain, the brother of former England cricketer Nasser Hussain, said: "Certain senior executives of GSK China who know our systems well appear to have acted outside of our processes and controls which breaches Chinese law."
GSK's eventual admission of guilt last July came a month after the company said a four-month internal investigation had found "no evidence of corruption or bribery in our China business".
The UK's Serious Fraud Office and the US justice department are being kept informed of the Chinese investigation.
He said pharmaceutical firms must end the decades-long standard practice of paying independent doctors to promote drugs, and make sure patients' interests come first.
"We recognise that we have an important role to play in providing doctors with information about our medicines, but this must be done clearly, transparently and without any perception of conflict of interest," he said.
In 2012, GSK paid a record $3bn (£1.9bn) in fines to settle claims that it tricked and bribed US doctors into prescribing children dangerous antidepressants.
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