By Mark Doyle
BBC world affairs correspondent
Confidential United Nations documents seen by the BBC say Rwanda maintains military control over parts of the Democratic Republic of Congo.
Congolese commanders deny taking orders from Rwanda
The alleged control - which Rwanda denies - is through proxy Congolese forces used by Rwanda.
The UN fears that a Rwandan invasion could re-ignite the war in the vast territory of DR Congo, a war which has destabilised much of Africa.
When contacted by the BBC, the UN office in DR Congo had no comment.
The papers could go some way to explaining how Rwanda can be accused by DR Congo of mounting an incursion without the UN being able to confirm the presence in DR Congo of regular Rwandan army troops.
The whole of central Africa is on a knife-edge as a result of a public threat by Rwanda to invade DR Congo to deal with anti-Rwandan government rebels which have bases in the Congolese mountains.
The United Nations fears that Congo's war, the deadliest conflict in the world today, could easily be re-ignited by such an invasion.
The papers say Rwanda maintains what the UN calls "Rwandan military structure of control" over parts of DR Congo through the use of proxy Congolese forces.
These forces are powerful.
In June, a renegade Congolese army chief seized the strategic Congolese town of Bukavu, on the border with Rwanda, in a move which led to widespread unrest throughout DR Congo.
According to the UN documents, the renegade Congolese army commander was "the military chief" of the Rwandan military structure of control and that, as recently as late last month, this structure remained in place.
Rwanda angrily denies any such allegations but asserts its right to pursue anti-Rwandan government rebels which have bases in DR Congo.
These rebels are accused by Rwanda of being the remnants of the army which committed genocide there in 1994 before the forces of the current Rwandan government chased them into DR Congo.
Rwanda says the rebels threaten a new genocide.
The fall-out from the mass killings of 1994 is, more than a decade later, still being felt throughout central Africa.