DAKAR, Senegal — Rwanda-backed rebels appeared to be heading toward a third major city in eastern Congo, residents said Tuesday, as international pressure rose over the M23’s expansion in a mineral-rich region that is critical for global technology.

The M23 rebels on Tuesday attacked all the main Congolese army positions on the road to Butembo, a city of 150,000 people, and the situation was rapidly deteriorating, said Auguste Kombi, a civil society leader in Kitsombiro, a town along the road.

“We’re afraid that the enemy will advance to Butembo,” Kombi said.

Butembo is about 130 miles north of Goma, the city of over 2 million people that the M23 rebels seized last month as about 3,000 people were killed.

The advance on Butembo means the rebels are spanning out both north and south of Goma. The rebels this week seized another provincial capital to Goma’s south, Bukavu, near Burundi. The region is rich in gold and coltan, a key mineral for the production of capacitors used in most consumer electronics such as laptops and smartphones.

Also Tuesday, the M23 captured the town of Kamanyola, about 15 miles south of Bukavu, after they overcame resistance from the Congolese army in the evening, said Steve Mubalama, a civil society representative in the town.

Mubalama expressed fears that the M23 rebels would advance a further 45 miles to the south to take the strategic city of Uvira.

The M23 is the most prominent of more than 100 armed groups vying for control of eastern Congo’s trillions of dollars in mineral wealth. The rebels are supported by about 4,000 troops from neighboring Rwanda, according to U.N. experts, and at times have vowed to march as far as Congo’s capital, Kinshasa, over 1,000 miles away.

“We’re worried because we’re in danger of experiencing a situation similar to that in Goma, with the loss of human lives,” said Kambale Nyuliro, a Kitsombiro civil servant. He told the AP that Lubero town, on the way to Butembo, was surrounded on three sides by M23 fighters but still under Congolese army control.

“Since the fighting began, the enemy has only advanced,” he said.