U.S. aircraft are coming back from most combat missions in Iraq without dropping any bombs, Chairman of the Joint Chiefs of Staff Army Gen. Martin Dempsey said Tuesday.

"At a similar period in the Afghanistan conflict in 2012, the number of aircraft that returned with their ordnance because there were not targets available on the ground was 83 percent," Dempsey told the Senate Armed Services Committee. "It's 65 percent in Iraq right now."

Dempsey was responding to Sen. Jeff Sessions, R-Ala., who was pressing Dempsey on why he has not recommended to President Obama that the U.S. embed joint terminal attack controllers with Iraqi troops to better coordinate airstrikes.

"The JTACs and the Special Forces observers are not a silver bullet to the destruction of ISIS," Dempsey said. "The silver bullet is getting the Iraqis to fight."

The head of Air Forces Central Command told reporters in June that many U.S. sorties end without a strike because Islamic State fighters have intermingled with civilians in both Iraq and Syria by operating near schools, mosques and other sensitive areas.

"There's never been a target that is easily available for a terrorist enemy that is wrapped around the population," Lt. Gen. John Hesterman said in a June 5 news briefing. "You have to unwind them from around a population and kill them where you can."

Still, Hesterman said he is comfortable with the rules of engagement for U.S. pilots.

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"Nothing stops us from self defense," he said. "If we see the enemy shooting at friendly forces or at us, we kill them right away."

Even if they do not strike targets, U.S. aircraft provide "persistent armed overwatch" in case they are needed to support ground forces, a spokesman for Air Forces Central Command said on Tuesday. The Islamic State fears coalition airpower, he said.

"Our presence has dramatically degraded their ability to organize and project significant combat power," said Capt. Andrew Caulk in an email to Air Force Times. "We've been able to impact the enemy while taking exceptional care to limit collateral damage and civilian casualties in the most precise air campaign in history."

But retired Air Force Lt. Gen. David Deptula argues that the Obama administration has "shackled" U.S. airpower to avoid any civilian casualties.

"Adhering to a zero civilian casualty goal is backfiring in ways that those who directed it probably did not intend," Deptula said in an email Tuesday to Air Force Times. "It is yielding to the Islamic State an air defense capability they do not have to pay for, equip to attain, or man to employ."

Any lives the U.S. has saved through restrictions on airstrikes are outweighed by the thousands of innocent people whom the Islamic State has killed, said Deptula, former deputy chief of staff for intelligence, surveillance and reconnaissance

"Our airmen are performing magnificently at the individual and unit level doing the most they can while encumbered with incredibly onerous rules of engagement — well in excess to the laws of armed conflict," he said. "Let's capitalize on our airpower advantage — not unnecessarily restrict it."

Rep. Martha McSally has also argued that U.S. pilots are under too many restrictions that have hampered the air war against the Islamic State.

"What we've seen and heard from those involved is that our forces continue to face restrictions on using our full air power to destroy ISIS, which is why I asked Gen. Dempsey this question a few weeks ago during a House Armed Services Hearing," McSally said in a statement to Air Force Times on Tuesday.

McSally, a former A-10 pilot, said earlier that she has heard that U.S. pilots have been forced to return to base because they ran low on fuel while waiting for permission to attack a target.

"While the administration is hoping that the Iraqi military will eventually gain the capabilities to defeat ISIS, hope is not a strategy," she said in Tuesday's statement. "The fact is, we have our own national security interests in destroying ISIS, and our unnecessary restrictions on air power are allowing them to continue to committee gruesome atrocities against innocent populations and threaten our security and that of our allies around the world."