An unknown gunman has shot and killed a son of a senior aide of President Gloria Arroyo after a traffic row in the Philippine capital, police said Thursday.

Renato Ebarle, 27, was at the wheel of a car when another motorist in a vehicle bearing licence plates reserved for foreign diplomats "alighted with a drawn firearm" and opened fire late Wednesday, killing the victim, they said.

Police launched a manhunt and were checking for possible political motives behind the attack, which they said took place after a brief verbal exchange between the suspect and the victim.

Police and relatives said the victim was the son and namesake of Arroyo's chief of staff, who carries the rank of undersecretary or the equivalent to junior minister.

The elder Ebarle and the president's office were not immediately available for comment.