A ceasefire deal was signed between the government, its allies and northern separatist groups last year, but violations have increased since pro-government fighters seized the flashpoint town of Menaka late last month.

Mali’s government and allied militia signed up to a U.N.-backed peace deal in March, but Tuareg-led rebels said more talks were needed, delaying international efforts to restore order to a zone awash with separatist and Islamist gunmen.

“The volatile security situation is hindering access for humanitarian workers to all affected areas and the growing insecurity in the region is making the provision of protection and assistance to the newly-displaced very challenging,” UNHCR spokesman William Spindler said in a statement.

Tens of thousands of people have fled their villages in Gao, Mopti and Timbuktu in northern Mali in recent weeks due to fear of violence or forced recruitment by armed groups, and many are sleeping outdoors, according to the UNHCR.

Hundreds of refugees have also crossed into neighboring Niger, Mauritania and Burkina Faso since the end of April.

The UNHCR said the violence has exacerbated tensions between villagers. Refugees who fled to Niger from a single village in Gao do not want to live in the same camp as they accuse each other of having links to opposing armed groups, the UNHCR said.

More than 100,000 people have been uprooted within Mali since conflict broke out between pro-government forces and rebel groups in 2012, while some 137,500 people have sought refuge in neighboring countries, according to the refugee agency.

Violence has continued in northern Mali despite a 2013 French-led intervention that pushed back al Qaeda-linked fighters who hijacked the Tuareg-led rebellion and seized two-thirds of the country in 2012.

The U.N mission in Mali said last week it was investigating reports of serious human rights abuses, including the execution of civilians in the north of the country.

Clashes last week killed at least six civilians, including a Malian aid worker, rebels and a local source said at the time.

In the latest sign of a flare up in the north of the country, three United Nations peacekeepers were wounded on Thursday when a vehicle in a convoy escorting their commander and the force’s police commissioner hit a landmine.

More than 35 U.N. troops have been killed in Mali since the mission deployed in mid-2013.