WASHINGTON  American military officers are expressing concern over the spreading use of makeshift bombs beyond the war zones of Iraq and Afghanistan to other countries in the region, as well as in East Asia and South America.

Improvised explosive devices, as the military calls them, have been the largest killer of American forces in Iraq and Afghanistan, showing up with devastating effect in Pakistan and India, but also with less notice in Thailand, Sri Lanka, the Philippines, Colombia, Somalia and parts of North Africa.

Even Russian security forces have faced the devices in the republics of Ingushetia and Dagestan, although attacks in Chechnya have fallen.

“There is a robust and constant I.E.D. effort among violent extremists who are using it as their weapon of choice,” said Lt. Gen. Thomas F. Metz, director of the Pentagon’s organization in charge of seeking ways to counter improvised explosives. “That won’t change for decades. We are in this fight for a long time.”