* City was seized and briefly held by rebels last year
* U.N.'s Ban due to visit Goma this week
Congolese soldiers clashed with rebel fighters for the first time in nearly six months on Monday near the city of Goma, just days before U.N. Secretary-General Ban Ki-moon is due to visit the troubled eastern borderlands.
Fighting began in the early morning after the Tutsi-dominated M23 rebels attacked government positions around 10 km (6 miles) north of mineral-rich eastern Democratic Republic of Congo's largest city, a military spokesman told Reuters.
M23 seized and briefly held Goma last November despite the presence of thousands of U.N. soldiers.
"The fighting has been with heavy weapons. It's still continuing although it is less intense ... We're sending reinforcements. We must protect the town of Goma at all costs," Colonel Olivier Hamuli said.
M23 spokesman Amani Kabasha said that M23 had initially driven off an attack by the FDLR, a Rwandan Hutu rebel group based in Congo's volatile east, before coming under attack from government artillery.
"We are not responding to their shelling, but what we're hearing is not good, that (Congolese president Joseph) Kabila is sending reinforcements. He needs to calm down," Kabasha said.
No casualty figures from the clashes were immediately available.
The fighting comes after months of stalled peace negotiations and as Tanzanian troops, part of a new U.N. brigade charged with neutralising armed groups including M23, began deploying in the east.
Ban is due to arrive in Goma this week as part of a visit with the president of the World Bank, aiming to draw attention to the conflict in Congo, where millions have died during nearly two decades of violence.