"Boko Haram's horrendous abuses, unspeakable cruelty, total disregard for human lives, and wanton destruction of property are unmatched," Dlamini-Zuma said in a statement after the bloc's Peace and Security Council met late Thursday, ahead of a full AU summit meeting on Friday.
The Boko Haram uprising has become a regional crisis, with the four directly affected countries -- Cameroon, Chad, Niger and Nigeria -- agreeing along with Benin to boost cooperation to contain the threat and to form a Multinational Joint Task Force (MNJTF).
"The continued attacks in northeastern Nigeria and the increasing attacks in the Lake Chad Basin, along the border with Chad and Cameroon, and in the northern provinces of that country, have the potential of destabilising the entire region, with far reaching security and humanitarian consequences."
More than 13,000 people have been killed and more than one million made homeless by Boko Haram violence since 2009.
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Regional nations pledged earlier this month to commit a battalion each to the force, a total of some 3,000 troops, but Dlamini-Zuma said after meetings Thursday it was decided that "no efforts should be spared" to defeat the fighters.
A key task of the force, to be deployed with an initial mandate of a year, will be "conducting military operations to prevent the expansion of Boko Haram and other terrorist groups activities and eliminate their presence," the statement added.
Nigeria has the largest army in west Africa but has come under criticism at home and abroad for failing to stop the advance of Boko Haram.