By Kieran Guilbert

DAKAR (Thomson Reuters Foundation) - A surge in violence in northern Mali and a spike in attacks on aid workers are hindering the delivery of food, water and healthcare to millions of people, aid agencies said on Wednesday.

Violent protests last week in the northern city of Gao raised fears that a peace deal signed last year between rival ethnic groups and the Malian government risks unraveling, threatening to plunge the nation into chaos.

There has been a resurgence of violence against aid agencies in recent months, with 10 attacks recorded in April and May after just three in the first three months of this year, according to data from the United Nations.

While most attacks involve the hijacking of vehicles, which is common in northern Mali, increased violence against aid workers is particularly concerning, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said.

"Aid agencies are not necessarily being targeted, but criminality prevails in some areas where they are acting," Anouk Desgroseilliers, public information officer for OCHA, told the Thomson Reuters Foundation by phone from the capital Bamako.

"This is restricting access and having an impact on the delivery of humanitarian assistance in the region," she added.

Around three million people in Mali do not have enough to eat, and some 500,000 in conflict-hit areas in the north need urgent food aid, according to aid agencies in the region.

Nearly 635,000 people lack access to clean water in northern and central regions hit by the violence, OCHA said.

Medical charity Medecins Sans Frontieres (MSF) said it was worried about a lack of health care in northern Mali, where few health centers are functioning and an outbreak of malaria has led to one in two people being infected in some villages.

Conflict in Mali erupted in 2012, when a loose coalition of separatist rebels and Islamist militants swept across the north of the country before a French-led military intervention in 2013 drove them from the main towns they had been occupying.

Islamist militants have since regrouped, targeting U.N. peacekeepers and French military forces stationed in the north, and launching high-profile attacks such as one on a Bamako hotel in November in which 20 people were killed.

The needs of local populations are acute, although the country's north is showing signs of recovery, MSF said.

"Economic activities are picking up, shops are reopening as people come back, but this is a post-emergency transition period so humanitarian needs are still very present," Sarah Chateau, MSF's head of mission in Mali, said in an interview.

The number of people uprooted within Mali has dropped by two-thirds to 37,500 since May 2015, but 135,000 refugees remain outside the country, mainly in Burkina Faso, Mauritania and Niger, fearful of returning home amid the violence, OCHA said.

(Reporting By Kieran Guilbert, Editing by Alex Whiting; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit