* Nigeria, Niger, others worried about Boko Haram
* Russia: Arms proliferation a result of Libya war
* Libya, Western envoys: Sahel problems pre-date war (Adds U.N. official, Russian and other envoys)
By Louis Charbonneau
UNITED NATIONS, Jan 26 (Reuters) - The Libyan civil war may have given militant groups in Africa's Sahel region like Boko Haram and al Qaeda access to large weapons caches, according to a U.N. report released on Thursday.
The report on the impact of the Libyan civil war on countries of the Sahel region that straddle the Sahara - including Nigeria, Niger and Chad - also says some national authorities believe the Islamist sect Boko Haram has increasing links to al Qaeda's North African wing. Boko Haram killed more than 500 people last year and more than 250 this year in Nigeria.
The U.N. Security Council met to discuss the report, which was prepared by a U.N. assessment team that met with officials from countries in the region. The discussion highlighted the deep divisions between Western powers and Russia over NATO's intervention in the North African oil-producing state.
"The governments of the countries visited indicated that, in spite of efforts to control their borders, large quantities of weapons and ammunition from Libyan stockpiles were smuggled into the Sahel region," the report said.
Such weapons include "rocket-propelled grenades, machine guns with anti-aircraft visors, automatic rifles, ammunition, grenades, explosives (Semtex), and light anti-aircraft artillery (light calibre bi-tubes) mounted on vehicles," it said.
More advanced weapons such as surface-to-air-missiles and man-portable air defense systems, known as MANPADS, also may have reached groups in the region, the report said.
U.N. special envoy to Libya Ian Martin, however, has told the Security Council that Libya's missing stocks of MANPADS have largely remained inside the country.
The report said some countries believe weapons have been smuggled into the Sahel by former fighters in Libya - Libyan army regulars and mercenaries who fought on behalf of former leader Muammar Gaddafi, who was ousted and killed by rebels.
Some of the countries told the assessment team that they had registered an increase in arms trade across West Africa.
"Some of the weapons may be hidden in the desert and could be sold to terrorist groups like al Qaeda in the Islamic Maghreb, Boko Haram or other criminal organizations," the U.N. report said.
'UNCONTROLLED SPREAD OF WEAPONS'
Lynn Pascoe, U.N. under-secretary-general for political affairs, told the Security Council that the new Libyan government insists many of the problems related to weapons and the Sahel originated when Gaddafi was still in power.
"Some of the problems are directly related to the fall of the Gaddafi regime in Libya but the nation's interlocutors emphasize that most of the problems are long-standing ones," he said.
British, French and U.S. envoys echoed the Libyan view that the problems existed long before the civil war.
Russia, which has criticized the toppling of Gaddafi and accused NATO of using a U.N. mandate to protect civilians in Libya as a springboard for regime change, said the U.N. report highlighted problems unleashed by NATO's intervention in Libya.
Russian envoy Alexander Pankin said the U.N. report confirmed that the "real consequences of the Libyan crisis, the real scope of which is only beginning to come to light, are a serious threat to security and stability in the entire region."
He said Moscow was especially concerned about "the uncontrolled spread of weapons in Libya and beyond its border."
The U.N. report said Nigeria was not the only country worried about the activities of Boko Haram. It said the group also was in Niger, adding that some governments believed Boko Haram members from Nigeria and Chad had received training at al Qaeda training camps in Mali in 2011.
"Although Boko Haram has concentrated its terrorist acts inside Nigeria, seven of its members were arrested while transiting through the Niger to Mali," it said, adding that they possessed documents about explosives manufacturing, propaganda leaflets and contact details for known al Qaeda members.
Links between al Qaeda and Boko Haram have become "a growing source of concern for the countries of the region," it said. (Reporting By Louis Charbonneau; Editing by Bill Trott)