The war on terror has prevented potential terror attacks on America, but the nation must remain on guard, Vice President Dick Cheney warned Tuesday night.

Cheney said terrorists are "being swept up in a worldwide roundup that is operating 24 hours a day."

"We have clearly disrupted their operations and no doubt prevented some planned attacks," he said.

Cheney was speaking at the International Republican Institute, an organization not affiliated with the Republican Party that teaches educational programs about democracy and assists with developing elections systems in more than 30 countries.

Cheney, with his wife Lynne Cheney, were at an IRI dinner to receive a Freedom Award.

Cheney said that the military has put a dent in operations of terrorists and airstrikes have cleared the way for ground attacks by U.S. Rangers and special operations forces.

"Terrorists and their supporters are, for the first time, beginning to worry about their own safety," he said. 

Cheney stressed the efforts the military is taking to avoid hurting civilians.  His emphasis came following reports from the Pentagon that over the weekend, three U.S. bombs went astray and two landed in a civilian neighborhood. Taliban rulers said more than 100 patients and medical workers were killed Monday when a bomb struck an elderly home.  The Pentagon said it had no information the number of civilian casualties. 

Cheney said that the Pentagon is doing its best to avoid such errors.

"Unlike the terrorists, we value human life and we do not target civilian populations," he said.

Cheney was introduced by Sen. John McCain, R-Ariz., a former Navy fighter pilot and one-time prisoner of war in Vietnam, who chairs IRI.

He joked about the amount of time the vice president has spent out of the public eye at a secret location since the Sept. 11 terrorist attacks.

"It's good to see you out again, having once been held in an undisclosed, secure location myself," said McCain.

Cheney's speech ended on a cautionary note.

"We have to assume there will be more attacks. That is the only safe way for to us proceed," Cheney said. "These last six weeks have brought a good deal of uncertainty and many changes into people's lives. Many of these changes are probably permanent, at least in the lifetime of most of us."

The Associated Press contributed to this report.