Fresh fighting in eastern DR Congo has forced hundreds to flee across the border into Rwanda, a day after a peace deal was signed in Washington DC.

Thursday’s agreement was meant to stabilise the resource-rich east but it has had little visible effect on the ground so far, in an area plagued by conflict for 30 years.

On Friday, fighters from the anti-government armed group M23 battled in South Kivu province with the Congolese army, backed by thousands of Burundian soldiers deployed alongside it.

Both sides are fighting for control of the border town of Kamanyola – where the Democratic Republic of the Congo, Rwanda and Burundi meet. M23 is now in control there.

Detonations that shook buildings echoed throughout the morning near Kamanyola, an AFP journalist reported in Bugarama, a border post on the Rwandan side about 2km (1.3 miles) away.

On Friday, the M23 accused the Burundian army of firing “without interruption” into the DRC.

A Burundian military source told AFP they were reinforcing their positions to ensure they were not overrun by M23 fighters and their Rwandan backers.

“The fighting is intensifying,” the source added, speaking on condition of anonymity. “There is a real risk the situation escalates. We are bringing reinforcements to the front because this is a red line for Burundi.”

The source said his country could not accept it if “the terrorists of M23 and their Rwandan backers reach Uvira”, a city in DRC less than 30km from Bujumbura, Burundi’s biggest city.

Lines of civilians fleeing the fighting crossed the border in the early hours watched by Rwandan police.

“The bombs were exploding above the houses,” said one witness, Immaculee Antoinette, from Ruhumba, near Kamanyola. “We were asked to remain locked inside our houses, but that seemed impossible.”

Hassan Shabani, an administrative official in Kamanyola, said schools, hospitals and civilian homes were all shelled.

On the Rwandan side, some residents were “scouring the hills from where the shots are coming, in small groups”, said a local woman, Farizi Bizimana. “The children and women are very scared and take refuge in houses when the gunfire becomes intense,” she added.

In January, M23 backed by Kigali and its army went on the offensive, capturing the major regional cities of Goma in North Kivu province and Bukavu in South Kivu.

On Thursday in Washington, DR Congo’s president, Félix Tshisekedi, and Rwanda’s president, Paul Kagame, signed an agreement that their host, the US president, Donald Trump, called a “miracle”.