Eleven people were shot dead in Cape Verde on Tuesday including eight soldiers, a local civilian and two Spanish citizens, state TV and police sources said.
The three civilians killed included two Spanish technicians on assignment in Cape Verde, according to the government. The deceased were all men aged between 20 and 51.
The suspected soldier is missing but there are "strong indications" he was behind the slayings, the former Portuguese colony's government said in a statement on its website.
The statement said "personal motives" inspired the attack, ruling out an attempted coup or any connection with violence associated with drug trafficking that has recently plagued the archipelago.
"People are advised to remain calm and serene," the statement said.
Cape Verde's battle against gangs smuggling Latin American cocaine to Europe has led to a series of reprisal shootings, though it was not known whether the killings were drug-related.
The country has worked with Western law enforcement agencies in its fight, including the US Drug Enforcement Administration.
Authorities in Cape Verde, which is classified as a developing nation, have received praise and financial aid from international bodies for their commitment to democracy and economic development.
However, the country has recently been fighting international drug rings attempting to smuggle cocaine into the country. Police last week seized 280 kilogramme's (600 pounds) of cocaine from a yacht, and officials have linked two recent armed attacks against public figures to that battle.
A new government took office last Friday after winning a March election and vowed zero tolerance in the fight against crime.