* Refugees report government forces, opposition clashes
* Around 3,500 Mozambicans refugees in Malawi camp
* Security experts concerned violence could worsen
* Unrest could deter investment in potential gas hub
By Joe Brock
KAPISE, Malawi, Jan 22 (Reuters) - When Mozambican troops hunting opposition fighters attacked his village this week, 10-year-old Wit Messenger turned and ran, leaving behind parents he may never see again.
Messenger is among thousands of Mozambicans who have fled across the border to refugee camps in Malawi in the last month, saying Frelimo government forces are burning homes and killing civilians in a campaign against Renamo guerrillas in an escalation of a simmering conflict between old civil war foes.
Spokesmen for both Frelimo and Renamo each told Reuters that the other side was responsible for attacks on their members in various parts of the country but would not give details about the violence that prompted the refugee exodus.
The first Mozambicans arrived in the Malawian village of Kapise in June last year but the U.N. refugee agency (UNHCR) says the flow of migrants has rapidly increased this month and predicts the number could rise from 3,500 now to 5,000 in coming days, more than it can currently handle. than half the refugees are children who walked for days from villages in Mozambique's western Tete province with just the clothes they were wearing.
"I could see the houses burning up ahead, then I heard the gunshots and I ran," said Wit, waiting with hundreds of other children to be given food in a sprawling hilltop camp of makeshift tarpaulin tents.
"I don't know if my parents are alive or dead. I'm scared I will never see them again," said Wit -- tearful, barefoot and wearing only a torn vest and ragged shorts.
Security sources say Renamo fighters have been attacking police outposts in recent weeks near the Malawi border, where they have public support, while Frelimo forces retaliate by torching villages where they believe rebels are hiding.
MEMORIES OF WAR
Renamo started out as a guerrilla force backed by neighbouring powers -- the white-minority government in what was then Rhodesia and later by apartheid South Africa -- to counter the communist Frelimo movement.
The latest violence has stirred memories of a civil war fought between Renamo and Frelimo from 1976 to 1992 in which a million people died and a further million fled to Malawi.
Some of the Mozambicans in Kapise told Reuters that they had hidden Renamo fighters because they felt they had no choice.
"Government were asking where we were hiding Renamo," said Agness Chifundo, who walked for two days with her seven children to reach Kapise. "When they couldn't find them they were burning houses and shooting. I saw five dead bodies and a woman was raped in front of me."
Tete province has large coal reserves but projects by companies such as Brazil's Vale VALE5.SA and mining giant Rio Tinto RIO.L have failed in recent years due to low prices, poor infrastructure and outbreaks of unrest.
Although the latest violence is far from the vast offshore gas reserves being developed off northern Mozambique by Eni ENI.MI and Anadarko APC.N , the violence is likely to worry investors already spooked by a global slowdown.
Though the full details of the clashes in Tete remain unclear and are likely to be disputed, there have been clear signs of growing unrest between Frelimo and Renamo.
Renamo's leader, Afonso Dhlakama, 63, has said he will in March seize control of six northern provinces, declaring autonomy in areas where his party won majorities in 2014's national election. He has not explained how this would be done but experts believe it would be unconstitutional.
Frelimo won 57 percent of the 2014 vote against 37 percent for Renamo. Renamo disputes the result and says Frelimo is to blame for the violence. Both sides say they are democrats but also resort to violence which they are unwilling to acknowledge.
ASSASSINATION ATTEMPT
Dhlakama has been in hiding since October last year following an assassination attempt he says was ordered by Frelimo, although the ruling party denies this.
Renamo's secretary general Manuel Bissopo was shot and wounded on Wednesday, hours after he accused security forces of killing members of his party. Frelimo says it was not behind the attack, in which Bissopo's bodyguard was killed. police presence in the capital Maputo has increased in recent days with officers occasionally stationed outside Renamo's office there.
President Filipe Nyusi, 56, says he wants to engage in peaceful negotiations with Renamo but Dhlakama has said this is disingenuous considering attacks on his members.
Few think Renamo has the capacity or desire to begin another all-out conflict but there is a high risk of more violence, security experts say.
"We've got a security problem brewing," one Maputo-based Western diplomat told Reuters. "We're seeing hits on senior officials and from what we're hearing the situation in Tete is bad. These refugees didn't up and leave for no reason."
The refugee influx is putting strain on Malawi's stretched resources at a time when one of the worst droughts in its history means 2.8 million people are expected to go hungry. has allocated Mozambicans some land in Kapise but it will not be enough. The UNHCR say the camps are already facing sanitation problems and there are fears of a possible cholera outbreak.
"We don't want to live like this but we cannot go back," Mozambican maize farmer Robert Keness told Reuters, pointing to pit latrines near tents packed with small children.
"We fear war at home."