* MNLA Tuareg rebels clash with army in Kidal for second day
* Officers involved in coup protest in southern barracks
* Dual challenge for new president after coup, occupation
* Al Qaeda's north African branch claims Timbuktu attack
Tuareg rebels battled soldiers in northern Mali for a second day and disgruntled army officers staged an unruly protest at a southern military base on Monday, underscoring the dual challenge facing the new government.
In the centre of the remote northern town of Kidal, MNLA Tuareg separatists traded fire with soldiers early on Monday before an uneasy calm returned. The fighting began on Sunday night, with both sides accusing the other of firing first.
In the southern garrison town of Kati, close to the capital Bamako, officers who participated in a March 2012 military coup fired into the air in protest at not receiving promotions they said had been promised.
Their former leader Amadou Sanogo was promoted from captain to a four-star general by a transitional government, in what diplomats said was an effort to encourage him to retire.
Around 30 officers went to the headquarters of Sanogo's Committee for Reform of the Armed Forces, fired into the air and took Sanogo's chief of staff away, according to one military source. The officers did not say what they intended to do with their "hostage", the source said, requesting anonymity.
President Ibrahim Boubacar Keita, elected on Aug. 11 with a pledge to reunite Mali after the coup, faces the dual task of reforming the ill-disciplined armed forces and ending a cycle of Tuareg rebellions in the north.
The coup, triggered by the government's failure to tackle a Tuareg uprising, ushered in an Islamist occupation of northern Mali which only ended when France launched a massive operation in January that killed hundreds of al Qaeda-linked fighters.
The resurgence in violence now threatens to derail peace efforts and complicate France's plan to reduce its presence in the West African country to just 1,000 troops by year-end.
The MNLA suspended its participation in the peace process on Thursday, accusing Keita of failing to honour a June ceasefire accord, after sporadic fighting in recent weeks.
The deal had committed Mali to opening talks on greater autonomy for the north within two months of the new government taking office.
AL QAEDA CLAIMS TIMBUKTU ATTACK
The clashes in Kidal followed a suicide car bomb attack near an army camp in the northern town of Timbuktu on Saturday in which the two attackers and at least two civilians were killed.
In a statement to Mauritania's Alakhbar news website, which has contacts with militant groups, a spokesman for Al Qaeda in the Islamic Maghreb (AQIM) - the organisation's north African wing - claimed responsibility for the attack.
The increase in violence poses a challenge for a U.N. peacekeeping force, whose deployment is being hobbled by lack of aircraft and troop commitments from members.
In Kidal, a resident who asked not to be identified said that fighters loyal to local chieftain Iyad ag Ghali had entered the town overnight. A military official, who also asked not to be identified, confirmed this.
Ag Ghali founded Islamist group Ansar Dine, one of three armed Muslim militant factions that seized control of the northern two-thirds of Mali last year. Ag Ghali's whereabouts has remained unclear since France launched its operation.