Local police chief Ghayoor Afridi said the assailants tried to kidnap the U.N. official and opened fire when he resisted. Two Pakistanis working for the U.N. were also wounded in the attack at the Kacha Garhi camp near Peshawar, he said.
The chief of the U.N. refugee agency in Pakistan, Guenet Guebre-Christos, said the dead U.N. worker was a 59-year-old Pakistani who had worked for the U.N. for 30 years. She said the other man killed in the shooting was a guard at the camp and did not work for the U.N.
The UNHCR later identified the slain official as Zill-e-Usman, a senior UNHCR National Staffer.
"The Taliban were likely involved in the U.N. shooting," a Pakistani security official told CBS News' Farhan Bokhari. "Early reports suggest that the gunmen were trying to kidnap him, probably to win the release of some of their people in custody."
On Monday, senior Pakistani officials warned that the remnants of Taliban militants who fought against the military in the country's northern Swat valley over the past three months were now expected to retaliate against government and relief officials.
Some 2 million Pakistanis have been driven from their homes in northwest Pakistan due to the military offensive against militants in the region - and many ended up in refugee camps. The violence led to a wave of humanitarian aid efforts by international organizations, raising the risk that relief workers could be targeted by militants.
Bokhari reports that a senior Pakistani official recently told reporters, "one major incident can easily upset the repatriation of the people from Swat."
U.N. employees and foreigners in Pakistan have come under attack several times in recent months.
Earlier this year, American U.N. worker John Solecki was kidnapped and held for around two months in southwest Pakistan by suspected Baluch rebels before being freed. His driver was shot dead.
Last month, there were U.N. employees among the 11 people killed in a suicide bombing that devastated the Pearl Continental Hotel in Peshawar.
In August of last year, Lynne Tracy, at the time the top U.S. diplomat in the northwest, narrowly survived an attack on her vehicle in Peshawar by suspected militants. In November, also in Peshawar, gunmen shot and killed American aid worker Stephen Vance.