WASHINGTON, July 23 (UPI) -- Host governments and combat advisers are the keys to a successful counterinsurgency strategy, not foreign military forces, a top U.S. military strategist said.

Retired Lt. Col. John Nagl, an adviser to U.S. Central Command chief Gen. David Petraeus, addressed the National Press Club in Washington, speaking on the need to employ the counterinsurgency strategy used in Iraq to deal with the declining security situation in Afghanistan, The Army Times said.

"It can be safely assumed that (Petraeus) will apply many of the lessons learned from Iraq to what has until recently been a forgotten war" in Afghanistan, Nagl said.

Nagl, who helped write the latest counterinsurgency manual for the U.S. military, said one of the most important lessons learned from the Iraq campaign is that foreign military powers cannot successfully win counterinsurgency operations.

"Foreign powers cannot win counterinsurgency campaigns, but they can enable and empower host nation governments to do so, and one of the most important tools they have to accomplish this task is the use of combat advisers," he said.

Carter Malkasian, a naval strategist who also spoke at the Washington event, said "self-defense" forces in Iraq contributed largely to the recent calm in Iraq following the U.S. "surge" strategy. He cautioned, however, that strategy was not yet implemented to its fullest potential in Afghanistan.

"The lessons of Iraq have not fully been transferred over to Afghanistan to learn how to do this the right way," he said.