* General sold guns to groups accused of massacres -UN
* Report comes as Congo suffers setbacks against rebels
* President Kabila under pressure to reform army
One of Democratic Republic of Congo's most senior army commanders has been selling weapons to rebel groups accused of carrying out widespread massacres, according to a U.N. report published on Wednesday.
General Gabriel Amisi commands Congo's land forces, which suffered a humiliating defeat after being driven out of the eastern city of Goma by rebel fighters on Tuesday, despite support from thousands of United Nations peacekeepers.
The report, written for the U.N. by a group of independent experts, says that Amisi oversees a network providing arms and ammunition to criminal groups and rebels who roam in the hills and forests of Congo's resource-rich but troubled east.
The M23 rebel group that seized Goma, however, was not among the armed bands named in the U.N. report as receiving weapons through the network.
"Gen. Gabriel Amisi oversees a network distributing hunting ammunition for poachers and armed groups, including Raïa Mutomboki," the report says in reference to a local militia accused of widespread atrocities.
The report also says that Amisi ordered that 300 AK 47 assault rifles be given to another armed group operating in eastern Congo, known as Nyatura.
Earlier this month a separate U.N. investigation said Raia Mutomboki and Nyatura, along with the Rwandan FDLR rebel group, had been responsible for the deaths of more than 260 civilians in a wave of tit-for-tat ethnic massacres in remote parts of North Kivu province.
According to the report by the so-called Group of Experts, ammunition is bought in neighbouring Congo Brazzaville, before being smuggled through the Congolese capital Kinshasa to the east by a close network of Amisi's associates, including members of his family.
Former rebel Amisi is a colourful figure and president of a top Congolese soccer team, as well as being one of the most influential people in the government of President Joseph Kabila.
"Between the demands of Amisi's command responsibilities and those of his racketeering and business dealings, the latter have always won out," Group of Experts head Steve Hege told Reuters.
Neither Amisi nor a spokesman for Congo's army - known as FARDC - were immediately available to respond to the allegations in the report, which already caused controversy by alleging that neighbouring Rwanda and Uganda are backing the M23 rebel movement, charges strongly denied by both governments.
Congo's army is famously ill-disciplined, and these allegations, coupled with M23's seizure of Goma, are likely to heap pressure on Kabila to push through military reforms.
On Tuesday, the army was driven out of Goma by M23 fighters, leaving a trail of corpses, burnt-out cars and abandoned equipment. M23, named after the March 23 rebel peace deal struck in 2009 and which it claims the government has broken, vowed to "liberate" all of Congo.
Previous U.N. reports have implicated Congolese soldiers in running lucrative mineral smuggling rackets and carrying out abuses against the civilian population.