General Jean Kahwaji announced the deaths as clashes between Lebanese troops and militants firing heavy machineguns and mortar rounds entered a second day in and around the town of Arsal in eastern Lebanon.
At a press briefing, Kahwaji warned that the situation was "extremely dangerous" and acknowledged the rising military toll.
"The army has lost 10 martyrs, with 25 more wounded, including four officers, and 13 soldiers are missing, possibly being held prisoner," he said.
The violence is the worst to hit the area since the beginning of the war in neighboring Syria in 2011.
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It erupted after the detention of a Syrian the army said had admitted to being a member of Al-Qaeda's Syrian affiliate, Al-Nusra Front.
Kahwaji said the man, Imad Ahmed Jumaa, had been scouting for an attack against the military in the area, and that the outbreak of fighting was premeditated.
The clashes began yesterday after gunmen angered by Jumaas arrest surrounded Lebanese army checkpoints before opening fire on troops and storming a police post in Arsal, security sources said.
The army warned yesterday of the seriousness of the situation and insisted it would "not allow any party to transfer the battle from Syria" to Lebanon.
"The army will be decisive and firm in its response and will not remain silent as foreigners try to turn our land into a field for crime and terrorism, murder and kidnapping."
The outbreak of violence sparked clashes in the northern city of Tripoli, where Sunni militants who back the Syrian uprising have regularly fought Lebanese security forces and residents from the Alawite sect who back Syria's President Bashar al-Assad.
The violence in Arsal prompted the US State Department to urge all parties to respect Lebanon's policy of "dissociation" from the Syrian conflict.
The United States "strongly condemns the attack," spokeswoman Jen Psaki said, vowing "strong support" from Washington for Lebanon's state institutions.