No one was hurt when the bus carrying 11 ethnic Albanians, three Bosniaks and one Serb, was hit with a rocket-propelled grenade on Sunday which pierced the passenger compartment but failed to explode.
The bus was part of a regular line running between the Kosovo town of Dragas and the Serbian capital Belgrade.
Jessen-Petersen instructed U.N. police to take "stringent measures to enhance security" including extra police patrols and vehicle checkpoints following Sunday's incident near the southwestern town of Prizren.