A U.N. police officer stands guard on a night patrol in the northern city of Timbuktu. The U.N. mission in Mali marks the first time a significant peacekeeping contingent has been sent to help a state regain control over areas contested by terrorist groups.

The United Nations was remarkably unprepared for the threat. Most of its troops from Africa and South Asia brought tanks and vehicles that were easy targets for explosives, unlike U.S. mine-resistant vehicles. The U.N. compounds, dotted with metal storage containers turned into offices­ and bedrooms, had flimsy perimeter security and were vulnerable to the massive car bombs used by al-Qaeda in the Islamic Maghreb (AQIM), the regional affiliate of the extremist group. For a while, U.N. forces­ didn’t have a single attack helicopter.

“We weren’t ready for these challenges,” said Mohamed El-Amine Souef, a native of the Comoros Islands who is the top U.N. official in Gao, a city in northern Mali. Last year, Souef’s compound was struck by a suicide bomber, the shrapnel battering his front door.

But the United Nations’ dilemma goes beyond a lack of preparation or anti-terrorism equipment. At its New York headquarters and around the world, diplomats are debating: Should U.N. forces be engaged in counterterrorism at all?

“It’s time for us to realize that this kind of front-line role is central to the future of the United Nations,” said Peter Yeo, a senior official at the U.N. Foundation, a Washington-based nonprofit organization that supports the goals of the world body.

Yeo and others argue that without a counterterrorism capability, U.N. peacekeepers can’t operate productively in many of the world’s war zones.

But critics say that such a role would violate the peacekeepers’ core principle of impartiality and ultimately make them less effective.

“Peacekeepers are only meant to use deadly force to protect civilians or to stop spoilers from threatening a peace process, not to pursue any group’s military defeat,” said Aditi Gorur, director of the Protecting Civilians in Conflict program at the Stimson Center, a Washington-based research center.