* Libya fears flows of militants back into country from Mali
* France launched military offensive in Mali against rebels
* Niger to allow U.S. to station drones on its territory
By Michelle Nichols
UNITED NATIONS, Jan 29 (Reuters) - A military intervention by France in Mali to combat Islamist rebels could exacerbate a "precarious" security situation in Libya, where armed groups have targeted security officials and diplomats, the United Nations said on Tuesday.
U.N. special envoy Tarek Mitri, head of the U.N. mission in Libya, said that country's government faced a serious security challenge in the east, where the U.S. ambassador and three other Americans were killed in September.
"The opposition of armed radical groups to the military intervention in Mali may exacerbate the situation given ideological and/or ethnic affiliations as well as porous bordering in Libya," Mitri told the U.N. Security Council.
A trigger for the Mali crisis was the return from Libya of heavily armed fighters once on the payroll of Libyan leader Muammar Gaddafi, say regional security experts. Rebels toppled Gaddafi's government in 2011 and he was captured and killed.
The former Gaddafi gunmen and the wide availability of arms during the Libyan conflict inflated the ranks of separatist and Islamist groups in Mali who launched attacks on the Malian army in early 2012 and took control of the country's north.
Libya is worried that if its vast desert borders cannot be secured there will be a flow of weapons and Malian and foreign Islamist fighters back through Algeria and across its borders as a French-led military offensive works its way north in Mali, winning back territory from the al Qaeda-allied militants.
"Security along Libya's borders remains a key concern given the current capacity limitations and the possible impact of recent developments in Mali," Mitri said. "The situation in the east poses a serious challenge to the government and threatens to derail its attempts to secure stability."
THREAT TO WESTERNERS, NEARBY COUNTRIES
Libya's foreign minister recently called for United Nations peacekeepers to be deployed in Mali to prevent uprooted fighters from destabilizing countries nearby.
"Senior Libyan officials whom I met recently stressed their concern over the situation in the east and pledged to provide better security to the diplomatic community and the citizens of Benghazi," he said.
Benghazi, cradle of the uprising against Gaddafi, has experienced a wave of violence against diplomats as well as military and police officers, including an attack in September that killed the U.S. ambassador and three other Americans.
Benghazi has been the scene of power struggles between various armed Islamist factions. U.S. intelligence officials say Islamist militants with ties to al Qaeda affiliates were most likely involved in the deadly Sept. 11 assault on the U.S. mission in Libya's second biggest city.
Niger has given permission for U.S. surveillance drones to be stationed on its territory to improve intelligence on al Qaeda-linked Islamist fighters in northern Mali and the wider Sahara, a senior government source said.
Last week European countries urged their nationals to leave Benghazi, with Britain citing a "specific and imminent" threat to Westerners days after a deadly attack by Islamist militants in neighboring Algeria. [ID: nL6N0AT821]
At least 38 hostages were killed in an attack on Algeria's In Amenas gas complex near the Libyan border earlier this month. An Algerian al Qaeda leader said it was a response to France's attack on his allies in Mali.
Security experts said the European warnings on Benghazi were probably in response to threats from groups angered by the French operation in Mali and inspired by the attack at Algeria. (Reporting by Michelle Nichols; Editing by David Gregorio)