UN peacekeeping forces have traditionally been only lightly armed and use minimum force in self-defense, or if armed persons try to stop them from carrying out their authorized tasks. UN military observers and civilian police are normally unarmed.

Peacekeeping faces its most difficult challenges when conflicting parties fail to live up to their commitments and fighting resumes; or when they purposely thwart peacekeepers' efforts. Peacekeepers have sought to stabilize such situations and to minimize suffering of non-combatants--often at great personal risk and despite unclear mandates and insufficient resources--primarily through persuasion and negotiation. At times, however, the peacekeepers' job has become all but impossible. The conflicts in Rwanda in 1994, in Bosnia and Herzegovina and in Somalia between 1992 and 1995 demonstrate the limits of peacekeeping where there is no peace to keep, and the dilemmas posed by combining peacekeeping and the use of force.

Once deployed, many operations have faced a difficult or hostile environment,where factions on the ground readily resort to threats or the use of force--and the threat of or resort to force has been an available option. During the 1960-1964 Congo operation, UN peacekeepers were authorized in 1961 by the Security Council to use the requisite measure of force to complete the removal of mercenaries who had contributed to the secession of the province of Katanga. In order to counteract foreign intervention that had led to the weakened position of the central Government, UN peacekeepers were drawn into violent exchanges with armed elements.

In more recent situations, the Council has sought to equip peacekeeping operations with a credible military capacity that has helped avoid the need to resort to force. In 1996, for example, in such a demonstration of "robust" peacekeeping, the UN Transitional Administration in Eastern Slavonia, Baranja and Western Sirmium (UNTAES) was outfitted with some heavy weapons as a deterrent. The Security Council also authorized Member States to provide close air support or other forceful action in support of the mission. In Sierra Leone, the UN operation combined strong political pressure with a strong military posture to dissuade one of the parties from resuming the military option. In July 2000, following a series of unprovoked attacks on UNAMSIL troops, and after exhausting all other options, UNAMSIL undertook a military operation to free more than 230 United Nations peacekeepers who had been trapped for over two months by forces fighting against the Government.

Just as a capacity to use force can deter attempts to hinder peacekeepers from performing their duties, recent experience has shown that civic action programmes aimed at improving the lives of people in the mission area can generate goodwill and serve as an incentive to the parties to cooperate with the peacekeepers. Peacekeepers in many missions have helped restore essential infrastructure, communications links and services damaged or destroyed during fighting. Today in Kosovo, for example, supporting these efforts constitutes one of the main responsibilities of the United Nations Interim Administration Mission in Kosovo (UNMIK).