Unknown gunmen shot dead a Tamil staff member of the Danish Demining Group in Sri Lanka's far north on Monday, the group said, the latest in a rash of aid worker killings on the island.

The shooting took place in the army-held Jaffna peninsula, which is cut off from the rest of the island behind rebel lines and has been beset by shootings in recent months and attacks on troops blamed on Tamil Tiger rebels.

Steen Wetlesen, country programme manager of the Danish Demining Group, said four staff members travelling to work on two motorcycles were chased by three people also on motorbikes.

"There were shots towards them. The backseat rider on one bike was hit in the bottom by a shot, so they stopped," he said. "The people pursuing followed the front bike and managed to catch up with them in the end and killed the driver."

Wetlesen said the group, which has 300 staff in Jaffna, had suspended its work on the peninsula to determine how to improve staff security.

"Four of our staff during the last two years have disappeared. Two of our staff members have now been killed," he added.

The killing comes just days after U.N. Under Secretary General for Humanitarian Affairs John Holmes visited the island and said it had one of the worst records in the world for aid worker safety in terms of the number of aid workers killed.