“We are here together to strengthen United Nations peacekeeping in concrete and meaningful ways,” Mr. Ban told the Leaders’ Summit on Peacekeeping, held at UN Headquarters on the margins of the annual high-level debate of the General Assembly.

The Summit, convened by President Barack Obama of the United States, comes at a time when peacekeeping missions are unprecedented in scale of operation and scope of mandates with 125,000 troops, police and civilian personnel in 16 operations spanning four continents.

Mr. Ban said the more than 120 countries currently contributing personnel disarm, demobilize and reintegrate ex-combatants; strengthen rule of law and security institutions; and promote human rights.

“These numbers show peacekeeping’s value,” he said, “but are also a sign of troubled times.”

Saying that “the demand for peacekeeping has never been greater,” he also said “the situations into which peacekeepers are deployed have never been more challenging, as tasks multiply and we face extremists, criminal groups and others who show no regard for international humanitarian or human rights law.”

To ensure that UN peacekeeping is up to these and future challenges, Mr. Ban spoke of the need “to act urgently, boldly and collectively” to have predictable and effective military capabilities, a qualified police personnel, including more female officers, and a standby reserve for tomorrow.

He also reminded the participants of the need to prevent and punish sexual exploitation and abuse, and said he counted on all troop- and police-contributing countries to act swiftly and decisively to hold perpetrators to account.

“Those who serve in peace operations must never prey on the people they are meant to protect,” he said.