The United Nations on Monday condemned the killing of a Filipino aid worker in the restive southern Philippines, but said the attack would not affect its food distribution efforts there.

The worker was helping the UN's World Food Programme deliver rations on Friday when a gunman attacked the agency's truck outside Marawi city on Mindanao island, where many armed groups including Islamic militants operate.

"WFP strongly deplores this act of wanton violence that has led to the tragic and senseless loss of life of an individual who was assisting in the delivery of humanitarian assistance," the agency said in statement.

The WFP said the man was contracted locally and not a full-time staff member of the agency.

The killing highlights the dangers humanitarian workers face in the south, where a long-running Muslim separatist rebellion is complicated by a proliferation of unlicensed firearms and clans fighting over political turf.

The WFP has been providing assistance to Mindanao since 2006 and distributes about 2,000 tonnes of food -- an average of 100 truck deliveries -- a month, it said.

In December 2008, another Filipino aid worker was killed when unidentified gunman attacked a WFP convoy in the south.

The agency said Monday it was aware of the risks involved in delivering food to Mindanao, and that its operations would not change because of last week's killing.

"As of press time, based on the evidence on the ground, WFP is treating this incident as an isolated case, and will do everything possible to ensure that operations in central Mindanao will not be hampered," it said.

The WFP stressed that it was routinely in touch with the government and the military to ensure safety of its personnel.

WFP country representative Stephen Anderson earlier told AFP it was too early to blame any group for the attack, after other press reports pointed to the separatist Moro Islamic Liberation Front (MILF).

The 12,000-strong MILF has been waging a decades-long rebellion for the establishment of an independent Islamic state in the southern third of the mostly Catholic country.