Gunmen raided a Guinea-Bissau army barracks housing an elite unit near the capital's airport on Sunday, sparking a gunbattle that left at least six people dead, an AFP correspondent and a military source said.
The pre-dawn attack is certain to add to tensions in the deeply troubled west African country, where a junta seized power in a coup in April.
Unidentified armed men launched the assault on at about 4:00 am (0400 GMT), but soldiers fought off the attack after about an hour of fighting, forcing the assailants to flee, witnesses said.
An AFP journalist at the scene said he saw the bodies of five attackers while a guard at the barracks was also killed, a surviving comrade told AFP.
A military source confirmed the attack but would not say whether there had been any casualties among the elite "red beret" ground force unit targeted in the raid.
Army vehicles were criss-crossing the capital in the hours after the raid, although an AFP journalist said the situation remained was calm.
There was no information immediately available about who carried out the attack, but observers said there was some anger in the military about a recent round of promotions.
Since independence from Portugal in 1974, the army and state in the chronically unstable nation of 1.6 million people have remained in constant conflict, and no president has ever completed a full term in office.
The instability has helped make Guinea-Bissau a hotbed of cocaine trafficking to Europe.
After the April coup, orchestrated by army chief of staff General Antonio Indjai, the junta that had seized power reached a deal with a group of political leaders to hand control over to a transitional government led by interim president Manuel Serifo Nhamadjo.
The coup interrupted a presidential election between the first and second rounds, and the transition deal calls for new polls in 2013.
But the ousted African Party for the Independence of Guinea and Cape Verde (PAIGC), which is excluded from the interim government, has refused to recognise it.© ANP/AFP