Members of the Islamic State of Iraq and Syria have mockingly altered a White House appeal by Michelle Obama on behalf of African kidnapped schoolgirls, after the militants captured a fleet of US military Humvee vehicles in Iraq last week.

The photoshopped picture of Michelle Obama holding a placard originally read #bringbackourgirls, in aid of 276 schoolgirls in Nigeria who were seized in April by the Islamic extremist group Boko Haram.

The Humvees will now be used against the democratic government of Iraq, which the United States installed as part of its invasion of the country to topple dictator Saddam Hussein in 2003.

Isis changed the wording on Obama's placard to read 'please bring back our Humvee' – mocking the United States over the missing military gear.

Isis wants to establish a hard-line Muslim Caliphate in the region, based upon strict sharia law with harsh punishments and scant rights for women - or anybody who disagrees with the ideology.

Meanwhile, in Nigeria, the missing girls remain in the hands of Boko Haram. The govenment leading the search claims it knows where the terror group has the children. But it is reluctant to launch a rescue mission over fears the girls will be harmed.