Two Europeans working for the United Nations were shot dead in Somalia's Puntland region.

Multiple sources identified the men as Simon Davies, a British citizen and former Scotland Yard officer, and Clement Gorrissen. France said Gorrissen was a French citizen, while other sources identified him as Canadian.

In an interview with VOA's Somali Service, Puntland President Abdiweli Mohamed Ali said a mentally ill security guard shot the two men Monday as they arrived at an airport in the city of Galkayo.

The president said the shooter was immediately arrested by police, and an investigation is under way.

The U.N. mission in Somalia confirmed both shooting victims worked for the UN Office on Drugs and Crime.   

The men had come to Puntland to help with the construction of a prison, according to Ali.

Last week, a new 500-bed prison, built with the help of the U.N. Office on Drugs and Crime, opened in Puntland's capital, Garowe.

U.N. Secretary-General Ban Ki-moon condemned the "cold-blooded" killings. He urged authorities to fully investigate the shootings and quickly bring the perpetrators to justice.

U.N. representative to Somalia Nicholas Kay said there can be no justification for such a callous attack. He said the United Nations remains committed to supporting the Somali people as they emerge from decades of conflict.