 Pakistan is the biggest contributor to the UN peacekeeping effort |
These militia groups were guilty of some of the worst human rights abuses during the Democratic Republic of Congo's long civil war.
The trading went on in 2005. A UN investigative team sent to gather evidence was obstructed and threatened.
The team's report was buried by the UN itself to "avoid political fallout".
These events took place in and around the mining town of Mongbwalu, in north-eastern Democratic Republic of Congo.
The Pakistani battalion of the UN peacekeeping mission deployed there two years ago and helped bring peace to an area that had previously seen bitter fighting between the Lendu and Hema ethnic groups.
Locals welcomed them, but the lure of the rich alluvial gold mines proved too much to resist for some, recalls the head of the miners' association, Liki Likambo.
"I saw a UN Pakistani soldier who came to buy gold from one of the gold negotiators here in Mongbwalu. I was there in the shop. I saw it with my own eyes."
Deals
Soon the Pakistani officers were doing deals directly with the FNI militia.
 The gold from mines run by militias went to Pakistani peacekeepers |
Evarista Anjasubu - a local businessman said he had known of transactions between Pakistani officers and two of the most notorious militia leaders called Kung Fu and Dragon who controlled the gold mines.
"They were already friends. I knew well. It was gold that was the basis of their friendship. So the gold extracted from the mines went directly to the Pakistanis. They used to meet in the UN camp in Mongbwalu, in a thatched house."
As the trade developed the Pakistani officers brought in the Congolese army and then Indian traders from Kenya.
Richard Ndilu, in charge of immigration at Mongbwalu airstrip, became suspicious in late 2005 when an Indian businessman arrived there and went to stay at the camp of the Pakistani peacekeepers.
Scandal
Alerted to this illegal trade by her officials, the District Commissioner of Ituri, Petronille Vaweka, went to Bunia airport to intercept a plane from Mongbwalu.
 |  "I was there in the shop. I saw it with my own eyes" Miners' association head Liki Likambo |
She said her way was blocked by Congolese army officers, who refused to allow her to inspect the cargo.
"I knew they had gold because the price of gold increased when the Indians went to Mongwalu," she said.
"When we wanted to verify what was inside the plane the pilot refused to allow us to enter the plane - me who was the chief, he refused! It was a big scandal."
When the UN was alerted to the allegations of gold trading by Human Rights Watch in late 2005, they instituted a major investigation by the Office for Internal Oversight Services.
What they uncovered was even more explosive.
Rearming
This is from a witness statement given to the UN by a Congolese officer engaged in the disarming of the militia in the nearby town of Nizi:
 The battle for mining concessions has cost countless lives |
"The officer expressed his regrets over the malpractices of a Pakistani battalion under the auspices of Major Zanfar. He revealed the arms surrendered by ex-combatants were secretly returned to them by Major Zanfar thereby compromising the work they had collectively done earlier.
"Repeatedly he saw militia who had been disarmed one day, but the next day would become re-armed again. The information he could obtain was always the same, that it would be the Pakistani battalion giving arms back to the militia."
This evidence was backed up by an interpreter working with the Pakistani battalion at Mongbwalu.
On arriving at the Officer's Mess, the interpreter found two militia leaders - known as Kung Fu and Dragon.
The interpreter said that the first question from Major Ali was to Kung Fu - asking him: 'What about the weapons I gave you? What about the weapons Monuc gave you?'
Stand-off
A UN investigation team arrived in Mongbwalu in August 2006.
At first the Pakistani battalion there cooperated with them. But when they attempted to seize a computer with apparently incriminating documents on it a stand-off ensued.
 The UN-found weapons were returned to militias in Mongbwalu |
The Pakistanis surrounded the UN police accompanying the investigators with barbed wire and put two armoured personnel carriers outside their living quarters at a nearby Christian mission.
Thoroughly intimidated, the investigators were airlifted out of Mongbwalu.
The Pakistani troops are replaced every six months and the BBC investigation concerns events that took place prior to the deployment of the current Pakistani battalion.
When we put the allegations of weapons trading to the head of the UN in Congo, Ambassador William Swing, he denied emphatically that peacekeepers had been rearming the militia.
"This I can categorically deny. What we have done is just the opposite. We have demobilised more than 20,000. We have taken in caches of arms. We have destroyed arms. We have done public burnings of these arms. And there is absolutely nothing to that allegation."
He says that the investigation into gold trading has yet to be completed.
A UN official connected with the inquiry told the BBC there seems to have been a plan to bury it, to avoid alienating Pakistan - the largest contributor of troops to the UN.
The UN in New York has refused to explain what took place or why, nearly two years after the allegations first surfaced, the Congolese people have no idea what action - if any - has been taken to discipline the Pakistani soldiers concerned.
Pakistan's foreign ministry said the UN had informed it of the allegations only on Tuesday, and they would be looked into.
