Evidence is increasing that foreign forces are being drawn into the conflict in the east of the Democratic Republic of Congo.
Eyewitnesses told the BBC Angolan and Zimbabwean troops were on the ground.
While journalists report that some of Laurent Nkunda's rebel fighters are in the pay of the Rwandan army.
This has renewed fears that the fighting will see a re-run of the five-year Congolese war, which involved nine nations, before it ended in 2003.
The war, which erupted in August 1998, was the largest on the continent in recent times.
It saw Congolese government forces supported by troops from Angola, Zimbabwe and Namibia.
They were fighting rebels backed by Uganda, Rwanda and Burundi.
Despite a peace deal, the presence of the world's largest peace force and UN-backed elections, the resource-rich east of the country remains unstable.
Some 250,000 people have fled the most recent violence which flared in August between government forces and rebels demanding protection from Rwandan Hutu rebels who fled to DR Congo after Rwanda's 1994 genocide.
According to a resident of Goma, who asked to remain anonymous for his own safety, there are soldiers supporting the Congolese government in the town who are Angolans
"We are seeing soldiers wearing Congolese army uniform here in town but they are not speaking the same language like us. They are unable to speak French, Swahili or Lingala - that is bizarre," he told the BBC's Network Africa programme.
"They are patrolling but unable to communicate with the population. These are speaking Portuguese," he said.
Experts say this evidence is not conclusive, since some Congolese troops, including a group known as the Katangan Tigers, fought in Angola during their civil war, and frequently converse in Portuguese.
Angola denies sending troops into DR Congo, although says it would support the government if called on to do so by the regional grouping, the Southern African Development Community.
A recent Zimbabwean army deserter told the BBC he had been part of a force that remained in DR Congo after the end of the last war in 2003.
"There are about 250 soldiers who were left behind without knowledge of other countries," he said.
"Those who were left there are there to do duties like guarding President Kabila and those mines where they have got some interests of our bosses."
He said he had been on duty in Goma and the mining centre Lubumbashi and soldiers were rotated about ever six months.
Meanwhile, Britain's Financial Times newspaper says soldiers from the Rwandan army have been fighting alongside General Nkunda.
Their reporter in eastern DR Congo interviewed former rebels and observers who said some soldiers were continuing to receive their Rwandan salaries while fighting with the general.
Rwanda has repeatedly denied sending forces into DR Congo.
But BBC Africa analyst Martin Plaut says similar statements were made during the early stages of the last war - and no-one doubts that foreign troops played a key role in that conflict.
Forces from Chad and Central African Republic were also involved in that conflict.