A Pentagon deal to grant one of America's largest military contractors immunity from harming soldiers and civilians in Iraq was a unique arrangement, according to Army Secretary John McHugh.

As previously reported in Huffington Post and the Oregonian, taxpayers may be on the hook to compensate more than 150 military veterans who claim that a Halliburton subsidiary knowingly exposed them to cancer-causing chemicals in Iraq.

As part of a lawsuit filed by 26 Oregon National Guard soldiers who claim that they suffered health problems through exposure to hexvalent chromium while patrolling a water treatment plant near Basra in Iraq, it was revealed that contractor Kellogg Brown Root demanded and received legal immunity in return for taking over the $7 billion project in 2003.

In the wake of the disclosure in early August, Rep. Earl Blumenauer (D-Ore.) demanded some answers about the deal, including whether other military contractors have been granted similar immunity deals.

On Tuesday, McHugh responded to Blumenauer, explaining that KBR has not asserted its claims under the contract's indemnification clause. And he added that no other Army contract with KBR, which most recently was awarded a $2.8 billion deal from the Pentagon, contains such a deal.

McHugh added that "no other Army contracts awarded since 2001 to other companies for services provided in a contingency operation contain indemnification provisions." McHugh explained that the Army considers the use of such provisions "only in extraordinary circumstances involving unusually hazardous risks."

And McHugh explained that "no congressional notification was provided in connection" with the indemnification provision.

READ the letter from Army Secretary John McHugh: