BAKU (Reuters) - Two soldiers in Azerbaijan shot dead four fellow servicemen and then killed themselves at a military base near the breakaway region of Nagorno-Karabakh, the defence ministry said on Friday. The ministry said two other soldiers were wounded in the shooting, which took place on Thursday and the motive behind the shooting was not known. It gave no further details. The independent Turan news agency said several senior commanders of an artillery unit were among those killed after the two soldiers opened fire in the officers quarters of the base, and that the attack was motivated by mistreatment. The base is located in the western Dashkesan region of Azerbaijan, close to the Nagorno-Karabakh frontline where Azeri and ethnic Armenian forces in trenches have observed a patchy ceasefire since 1994. Azerbaijan has used revenues from oil exports to boost defence spending in a bid to tip the balance in the festering conflict over Nagorno-Karabakh, which broke away from Azerbaijan with Armenian support as the Soviet Union collapsed. But analysts say military reform has lagged far behind, and in a 2008 report the International Crisis Group thinktank said that corruption, nepotism and mistreatment were common in the poorly-paid conscript army. The ICG report said the situation in frontline units was particularly difficult, with no effective officer or military unit rotation system and units filled with conscripts too poor to escape the draft or arrange to be sent elsewhere.