As a new rebellion in the Democratic Republic of the Congo's war-torn North Kivu province perpetuates the cycle of violence that has plagued the region for decades, it is not only the local population that has been trapped in the crossfire. Virunga national park, home to the critically endangered mountain gorilla, is now also hosting warring rebel factions and government troops, with potentially disastrous consequences for the animals and communities in and around the park.

"This part of the park is now effectively under rebel control," says Emmanuel de Merode, director of Virunga park since 2008, when CNDP (National Congress for the Defence of the People) rebels were also in the area. The CNDP fighters were integrated into the army in 2009, but in May they mutinied and launched a new movement called M23. The rebels made significant advances this month, and now control Rumangabo, where the Virunga park headquarters are located.

The M23 rebellion has forced the park authorities to shut down what was a fast-growing tourism trade. In 2009 the park received 550 visitors; last year 3,000 tourists came to Virunga and that figure was projected to rise to 6,000 in 2012.

"Tourism is a huge part of the park's financial sustainability," says De Merode. "Just look at Rwanda. Ten years ago they had no tourism industry, but now their tourism industry contributes $430m to the Rwandan economy." Tourism could be a pillar of the Congolese economy. In Kenya in 2011, tourism brought in around $3.5bn, which equates almost exactly to all of Congo's 2011 budget receipts (pdf).

The collapse of tourism revenue is not just a problem for the park's funding. For the past two years, park authorities have contributed 30% of their gross revenues to projects in the impoverished surrounding villages. Engineer Naris Kikwaya has overseen the construction of schools, a health centre in Kabaya, and a system of fountains to deliver water to villagers in Kayenzi. These projects will be threatened if the park does not make money.

"I'm very happy with the water fountains that have been put up here," says one woman from Kayenzi. She insisted on anonymity, as did every person in the village who spoke to the Guardian. As a taxi motorcycle sped by carrying M23 fighters, it was clear why they were afraid to talk. "Before, it took a long time to fetch water. With the fountains I can do more work in the house, and my husband can spend more time in the fields. Before we couldn't send the children to collect water as it was too dangerous, but now it would be OK, if the rebels weren't here."

The villagers of Kayenzi send their children to the school recently built in Rumangabo using money generated by the park. "In Congo, each parent in a village has to contribute money to build a school," says one local man. "But here the school was built for us, which saves us a lot of money and means our children can be educated."

The fighting risks not only current but future tourism revenues, and therefore project funding, by threatening the assets that draw visitors to the park. "At the moment it's very difficult to know how the mountain gorilla population has been affected [by the conflict]," says De Merode. "There has been a lot of shelling in the area where they are, as well as bombing by the Congolese army and [the UN stabilisation force in Congo], which obviously brings a risk."

To De Merode's relief, the rebels and government forces this week agreed to allow a team of 45 rangers to search for and monitor the mountain gorillas. The Virunga park authorities said some of these gorillas have not been seen for over 10 weeks. There was further heavy fighting in the area this week, heightening fears for the gorillas' safety.

Despite the frequent conflicts in and around the park, the mountain gorilla population has doubled since 1992, making the conservation project in Virunga "one of the most successful endangered species programmes in the world", according to De Merode. "There are around 210 mountain gorillas in the park, which is roughly a quarter of the world's population," he says.

Park rangers are optimistic that the return of peace will bring the tourists back. "We are lucky that there is a strong tradition and culture of wildlife protection in this part of the world," says De Merode. This has helped to limit damage done to the park and its animal inhabitants by competing armed groups. "After all the work we have done it is frustrating and a shame [to suspend tourism], but when the fighting ends we'll start again."

For the villagers, though, the fighting means more than just an end to international visitors. "M23 have forcefully recruited boys as young as 12, they pillage our homes and they arrest anyone who complains," says a local man. "We know that tourism has paid for the water fountains and the school, and we do not want that to end. But above all we want to be sure of our security."

Moments later, a truck pulls around the corner and heavily armed M23 soldiers spill out of it on to the street – a timely reminder of what a distant prospect that security is.