NEW YORK (AP) — The top U.S. military official warned Tuesday that the world risks becoming immune to the suffering caused by escalating global security threats.

Army Gen. Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, said it would be "a historical shame" if the world doesn't realize it is reaching a point where it becomes insensitive to the magnitude of the problems caused by international crises.

"The world is at genuine risk of becoming immune to suffering, and if that happens I don't know where it stops," Dempsey told several dozen ambassadors and military attaches at an event sponsored by the U.S. Mission to the United Nations.

He urged world leaders and governments to "shake ourselves back into the reality that we can do something about it."

"In my 41 years of military service, I've never witnessed such significant shifts in the international security environment as we are seeing all around us today," he said. "The complex array of threats and, let's call it geopolitical jockeying, requires all of us to contend with an unpredictable landscape."

Dempsey, who will be stepping down and retiring on Oct. 1 after four years as the top military adviser to President Barack Obama, said today's security challenges cut across geography, diplomacy, economics and ideology with no clear-cut boundaries, making them difficult to contain.

He said the U.N.'s peacekeeping operations must keep pace.

"Peacekeeping operations are under greater strain than ever before," Dempsey said. "Simply stated, a disproportionate responsibility is being borne by some few to ensure the stability and security of so many. This imbalance is unsustainable."

He called for greater political and diplomatic backing from the 193 U.N. member states to ensure the viability of U.N. peacekeeping, which currently involves more than 120,000 peacekeepers deployed in 16 far-flung operations.

The United Nations does not have a standing army, but Dempsey urged the creation of rapid reaction forces and called for more highly skilled military and international police personnel. He also urged governments to provide more sophisticated equipment "or else risk failure of ongoing — and future — U.N. peacekeeping missions."

Dempsey said Obama will be co-hosting a summit on peacekeeping with Secretary-General Ban Ki-moon and several other world leaders on the sidelines of the annual ministerial meeting of the General Assembly in late September to "solidify the commitments needed to ensure an increasingly capable and reliable U.N. peacekeeping mission."