The United Nations refugee agency says more than 30,000 Nigerians fled the border town of Rann over the weekend to seek safety in Cameroon as attacks by Boko Haram extremists continue.

Spokesman Babar Baloch said Tuesday that thousands more have fled to neighboring Chad because of the violence in northeastern Nigeria.

Refugees began fleeing to Cameroon earlier this month when extremists attacked and seized Rann, in Borno state, on Jan. 14.

Increased violence in Borno also has forced 80,000 civilians to seek refuge in overcrowded camps or towns inside Nigeria. The refugee agency says the violence is not abating and is forcing aid workers to pull out of some areas.

The U.N. calls on countries in the region to keep borders open.