The Lord’s Resistance Army (LRA) rebel force has abducted 217 people since January in the Central African Republic (CAR), a campaign group says.
This is nearly double the number of abductions carried out by the LRA in 2015, LRA Crisis Tracker added.
The abductees, including 54 children, may have been forced to become soldiers or sex slaves, it said.
The LRA appear to be trying to “replenish” its forces because of military setbacks, the group added.
It has been hit by a spate of defections, and arrests since foreign forces began pursuing it in 2011.
The US deployed 100 special forces to support thousands of African troops searching for LRA commanders.
The International Criminal Court has issued an arrest warrant for its leader, Joseph Kony, to stand trial for war crimes.
The LRA had lost a “large chunk of its fighting force”, and seemed to be trying to rebuild its force through abductions, said Sean Poole of the Invisible Children campaign group, which is part of LRA Crisis Tracker.
The spike in abductions in the first three months of this year signalled a “huge change in the modus operandi” of the LRA, he told the BBC’s Newsday programme.
The LRA was formed in northern Uganda nearly three decades ago, but retreated to CAR and other countries as it came under military pressure.
LRA Crisis Tracker says it is responsible for more than 100,000 deaths, and a similar number of abductions.