He added that the convoy had stopped before the attack after one of the trucks broke down, and there are suspicions that local villagers then tipped off the rebels.
Panesa said Philippine soldiers were scouring the area for a wounded NPA rebel who was apparently left behind after the clash, while helicopter gunships were on standby to help wih the search..
In a separate incident on Monday a senior police official was shot dead in his car as he drove to work near Legaspi city, southeast of the Philippine capital of Manila.
Reports said three men wielding assault rifles shot superintendent Narciso Guarin, the deputy police chief of the Bicol peninsula, an impoverished area known for NPA operations.
NPA rebels withdrew from peace talks in 2004 after accusing the government of instigating their inclusion on US and European Union terrorist lists.
General Hermogenes Esperon Jr, the Philippine's military chief, said last month the armed forces were on track to crush the insurgency in two years.
He said the number of rebel fighters dropped from 5,781 in December 2007 to 5,470 so far this year because of battlefield losses, surrenders and desertions.