A top U.S. military official says the U.S. mission against a violent central African rebel group is likely to last for months but has no specific timetable.

President Barack Obama announced this month that he is sending 100 U.S. military personnel to help central African governments fight the rebel Lord's Resistance Army.

Defense and State Department officials defended the program Tuesday before lawmakers on the House of Representatives Foreign Affairs Committee.

Alexander Vershbow, the assistant secretary of defense for international security affairs, said the operation is limited to helping regional governments collect and use intelligence more effectively against the LRA.

He also said the Obama administration will review the effectiveness of the operation in several months.

Some lawmakers at the hearing expressed concern that the mission might grow in size, length and cost.

The LRA, once based in Uganda, is accused of attacking villages across three other African countries over the past few years, killing and kidnapping hundreds of people.

The group is notorious for kidnapping people for use as soldiers or sex slaves. Three of the group's leaders, including top leader Joseph Kony, are wanted by the International Criminal Court for alleged war crimes and crimes against humanity.