KAMPALA (Reuters) - Uganda has detained more than 100 former M23 rebels trying to return to neighboring Democratic Republic of Congo, breaking a deal to demobilize after their defeat in 2013, the government said on Thursday.

The former fighters, who had been staying in Ugandan camps after years of fighting in chaotic eastern Congo, were picked up in west Uganda in the region of Mbarara as they tried to sneak into Congo in disguise, the government spokesman said.

Congo’s government reported the rebel moves last week amid mounting opposition to Congolese President Joseph Kabila, who has decided to stay in office beyond his mandate that expired last month. Protests have raise fears of a civil war.

“The Uganda Security intercepted four vehicles at Mbarara that were carrying 101 former M23 combatants who were traveling on their way to Democratic Republic of Congo,” spokesman Ofwono Opondo said in a statement.

He said the former fighters had been detained after they were caught trying to disguise who they were, adding that the ex-rebels were violating a deal reached in 2014 for them to stay in the Ugandan camps.

Uganda was initially dismissive, with a minister telling Reuters this week he didn’t know or care if the rebels went missing. Thursday’s statement was Uganda’s first confirmation of the movement.

“That confirms the information that we had since three days ago,” said Congo’s Foreign Minister Leonard She Okitundu. “For us, it’s a good thing. It shows that the Ugandan government is willing to cooperate with Congo to avoid any armed incursions.”

Opondo said 270 former M23 fighters were still at Bihanga Barracks in Uganda, but added that a separate group of 40 had escaped a week ago and their whereabouts was still unclear.

The rebels had been in camps for demobilized fighters in Uganda following their defeat. Formerly, the M23 was the largest of dozens of armed groups in the country and controlled huge swaths of Congo’s mining heartland in the east.