The number of American — and Iraqi — fatalities from bomb attacks is rising as insurgents in Iraq receive deadly tips from outside sources.

In some cases, insurgents' "tactics have become more sophisticated" by relying on bombmaking experts from the old Iraqi Army and other countries, Lt. Gen. John Vines told reporters in a telephone call from Iraq.

"There is no discretion; they are hitting everything," adds Tech Sgt. Travis Brewster, of Hill Air Force Base's 775th Explosive Ordnance Disposal Flight, which dismantles bombs in Iraq and around the world. "They are not just necessarily going after the Americans."

Bomb attacks against American forces are at their highest levels since the United States first invaded Iraq in 2003. Since the beginning of combat, six servicemen from Utah have died from improvised explosive devices, car bombs and suicide bombers. Others have died from other causes and in accidents.

So far in June, at least 35 Americans have been killed by improvised explosive devices, or IEDs, according to Iraq Coalition Casualty Count, a Web site that tracks official figures from the Department of Defense.

But the insurgents are not just attacking Americans. In May, IED attacks against Iraqi civilians reached unprecedented levels, Vines said. At least 15 people died Thursday when four car bombs exploded in Iraqi neighborhoods.

The insurgency is not backing down. The top American commander in the Persian Gulf told Congress this week that the Iraqi insurgency is just as active as it was six months ago.

Gen. John Abizaid told the Senate Armed Services Committee, "We see good progress in both Iraq and Afghanistan. But we are realistic, and we know that great change is often accompanied with violence. We are not trying to paint a rosy picture."

At least 480 car bombs have exploded in Iraq since the handover of the sovereignty on June 28, 2004, according to an Associated Press count. At least 2,174 people have been killed and 5,520 have been wounded.

The insurgents are proceeding through the "natural progression of the bomber's evolution," Brewster said: The bombs are changing as the insurgents gain more knowledge and have access to more technology.

"These terrorists are very intelligent people," said Master Sgt. Mike Pitts of the 775th. "They try to change the way they do business so their improvised explosive devices have a better probability of working."

Hill Air Force Base employs the second-largest explosive ordnance unit in the entire Air Force. Members of the 775th are "nonstop deployed," Pitts said, dismantling and safely disposing bombs in Iraq and other world hotspots.