ABUJA, Nigeria (Reuters) -- Nigeria's army has posted two divisions to hunt for 200 schoolgirls abducted last month by Islamist rebels in an attack condemned globally, including by U.S. first lady Michelle Obama on Saturday.

The soldiers are stationed in the northeastern border region close to ChadCameroon and Niger to work with other security agencies, said Gen. Chris Olukolade, spokesman for the Defence Headquarters.

"The facilities of the Nigerian army signals as well as all the communication facilities of the Nigerian police and all the services have been devoted into coordinating this search," Olukolade said in a statement.

"The major challenge remains the fact that some of the information given here turned out in many occasions to be misleading. .... Nevertheless, this will not discourage the collaborative efforts that are on-going," he said.

Meanwhile, kidnappers in southern Nigeria's Niger Delta region released three Dutch nationals held since May 4, Anka Mustapha, a spokesman for Bayelsa state's Joint Task Force, which includes the military and police, told Reuters Saturday.

The kidnapping of expatriates by armed gangs seeking ransom money has been rife in the oil-producing Delta region, although it has tailed off since a 2009 amnesty was signed with militant groups there. Foreign companies have also improved their security.

Michelle Obama took the rare step of delivering her husband President Barack Obama's weekly radio address on Saturday to express outrage over the kidnapping.

"Like millions of people across the globe, my husband and I are outraged and heartbroken over the kidnapping of more than 200 Nigerian girls from their school dormitory in the middle of the night," she said in the address.

"This unconscionable act was committed by a terrorist group determined to keep these girls from getting an education - grown men attempting to snuff out the aspirations of young girls," she said.