In the third of a four-part series on the Democratic Republic of Congo, the BBC world affairs correspondent Mark Doyle continues his journey in the east of the country.
When I arrived at the marketplace in this small mountainside town, there seemed to be more than the usual number of armed men and boys milling around.
There have been mass militia killings on both sides of the Rwandan border
Dressed in an array of uniforms and civilian clothes, the men and child soldiers had the usual collection of AK-47 assault rifles, rocket launchers and mortar tubes slung over their shoulders.
After travelling in the DR Congo for several days I had become used to seeing armed men on the streets.
But here were hundreds in a single place - something was up.
I soon learned that the motley soldiers in Walungu marketplace were Mai Mai militiamen - a nationalist Congolese government reserve created to face rebellions and occupations by foreign armies far too widespread and numerous for the army-proper to handle.
The Mai Mai are fiercely nationalistic and implacably anti-Rwanda.
They see Rwanda as the root of Congo's problems because of its direct interventions and support for proxy anti-Kinshasa militias. Many households in eastern Congo have given one of their children to the Mai Mai, seeing this as a patriotic duty.
"Mai-Mai" means water - magic water, as one of their number explained to me, which, when applied, can protect a soldier from bullets.
The troop concentration in the marketplace was a symptom of a dangerous new phase in DR Congo, a country teetering between war and peace.
This group were being rotated out of the region to be replaced by soldiers of the Forces Armees de la Republique Democratique du Congo, or FARDC.
United Nations military sources said the troop rotation, ordered by the transitional government in Kinshasa, had been encouraged by the UN because the Mai Mai in this part of Congo were causing serious security problems.
These problems came to the fore recently when DR Congo and neighbouring Rwanda signed a new peace deal under which the two countries agreed to disarm militias hostile to the other.
Under the deal Rwanda would disarm some anti-Congolese government groups which it has backed, and DR Congo would disarm Rwandan rebels with bases inside DR Congo.
The Rwandan rebels concerned are the Forces Democratique pour la Liberation du Rwanda or FDLR. This group was originally formed from the remnants of the defeated ethnic Hutu Rwandan army which orchestrated the genocide of Tutsis and Hutu government opponents in Rwanda in 1994.
On a military map in a UN command tent in Walungu, FDLR territory is marked out in neat red lines - a large swathe of territory south-west of here.
But the neat military map is more hopeful than realistic; no-one really knows where all the FDLR forces are, and the breathtakingly beautiful mountains of this region are perfect guerrilla country. If insurgents want to hide here, they can with ease.
Under a new, tougher mandate from the UN Security Council, the UN forces in DR Congo are now supposed to help the nascent government army - the FARDC, which is made up of elements from all the former warring factions - to disarm the Rwandan Hutu rebels of the FDLR.
The Mai Mai are being moved from Walungu because they are suspected of collaborating with the FDLR.
This is hardly surprising.
The Congolese government used the Rwandan Hutus on many occasions during the war to oppose Tutsi-dominated Rwandan government army units which attacked DR Congo. Many Mai Mai therefore see the FDLR as their allies.
Under the new deal between Rwanda and DR Congo - which if it works will be a major step forward in the peace process for the whole of central Africa - the UN has decided to help DR Congo fulfil its part of the bargain.
The Rwandan army, UN officials argue, is well-enough organised to keep its side of the pact; the shattered Congolese forces, on the other hand, need help.
This is why, when I travelled through the dramatic landscape outside Walungu - with its majestic mountains and rugged passes - I saw patrols of Uruguayan UN peacekeepers with Congolese government soldiers prominently there beside them.
DR Congo's majestic mountains are ideal hide-outs
A UN official described the message being sent by these mixed patrols: "The signal to the Hutus is this", the official said bluntly, "disarm voluntarily now, or the new Congolese government army, with logistical backing from the UN, is coming to get you."
"The first phase of the exercise", said a Congolese FARDC officer known in Walungu as le Capitaine Jean-Paul, "is the voluntary phase".
"It will last for two months. If the FDLR don't cooperate, we will then proceed to the next phase, which is the use of force."
The development of the mixed UN-Congo government army patrols is highly dangerous, and for several reasons.
The main one is that the FDLR has said it will not disarm.
According to a well-informed military analyst in this region, the Hutu FDLR, far from being the ragtag marauding militia they are sometimes portrayed as, are in fact a well-organised unit with impressive military command and control.
"They're one of the most effective armies in this region" said the military analyst, who asked not to be named.
"They are well armed and their communications are also good. At the level of their political leaders they have satellite phones. At the brigade [large army unit] level they have working high frequency radios."
The FDLR also has strong political motivation - they want to return home to Rwanda to operate as a political party. For the Tutsi survivors of the genocide, this is, of course, out of the question.
For Hutus who say the Tutsis now operate a fascist state, their return is just a dream. The FDLR claims that 10 years after the genocide, many of their number in fact had nothing to do with the pogroms - that they should be given political space in Rwanda.
One UN official argued that most of the FDLR are in fact the descendants or relatives of Hutus who fled the advancing Tutsi army in Rwanda after the 1994 genocide and then took refuge in DR Congo.
Although some of them may well have been involved in the 1994 genocide, he said, their more recent memory was of the mass killings of Hutus by the Rwandan army and their proxies during the 1996-2000 war inside DR Congo.
Will the UN fight?
However, these realities are sometimes difficult for the international community to deal with politically, because it is still reeling from the guilt of having failed to stop the genocide - despite ample knowledge, at the time, of what was going on.
This guilt translates into far less pressure on the Rwandan government to share power than there is, for example, on DR Congo.
For these reasons, disarming the Hutu in DR Congo is a political obstacle course as well as militarily difficult.
The military analyst with knowledge of the FDLR said he assessed them, on their terrain, as more effective than most of the current Congolese government army.
In addition, there is always a political question mark over whether UN soldiers - however good they may be technically - will fight.
So it may also be that the FDLR are more effective, in their own military terms, than the UN.
The next two months may see dangerous days.