NATIONAL HARBOR, Md. – The intermingling, often overlapping, areas of Syria controlled by President Assad, the Russians, U.S.-backed rebel groups, and the Islamic State terrorist group are creating a monumental challenge, said the head of Air Combat Command Tuesday.

"This is not Desert Storm, this isn't Iraqi Freedom or Enduring Freedom; this is a totally different and incredibly complex battlefield with coalition airpower in a very, very challenging environment," said Gen. Herbert "Hawk" Carlisle at the Air Force Association's Air, Space and Cyber conference here,

The difficulty has been highlighted in the past few days by two incidents: an airstrike on a United Nations humanitarian aid convoy en route to the besieged city of Aleppo Monday, reportedly by the Russians, and an accidental strike Saturday on Syrian government forces, reportedly by U.S. aircraft.

In regard to the attack on the convoy, CENTCOM officials have confirmed that aircraft from the U.S. and its allies didn't conduct any bombings in the vicinity at the time it was hit, according to Col. Patrick Ryder, an Air Force spokesman.

The airstrike hit the convoy as it was headed for Aleppo, in the northwestern part of Syria, to deliver badly needed food, supplies and medicine to the city, which has been at center of the Syrian civil war since it began. The incident is estimated to have killed more than 20 people, and the U.N. announced it is suspending any further planned humanitarian convoys into the area.

The attack effectively ended a week-old cease-fire agreement that had been in place.

Russia — which is supporting the government of Syrian President Bashar al-Assad — denied conducting the airstrike. But several Syrian rebel groups, accused the Russians of carrying out the strike. The convoy likely would have provided aid to areas controlled by insurgents trying to overthrow Assad's regime.

CNN reported Monday afternoon that U.S. officials have reached a preliminary conclusion that Russia did carry out the airstrikes, but Air Force Times has not independently verified this.

Transparency lacking

Carlisle said Tuesday that Russia is not being transparent enough with its operations in the country. Although U.S. and Russian military officials communicate every day, that doesn't always amount to a disclosure of Russia's planned military actions in Syria.

"The Russians are the Russians, I don't know how else to say it," Carlisle said. "They're sometimes very forthcoming, other times less so."

He pointed to examples where Russia has launched military operations with very little notification.

"There have been cases in the past where they've launched cruise missiles through airspace, uncoordinated, with the potential for challenges there with respect to where coalition aircraft were flying or not flying," Carlisle said.

The U.S. and Russia are still in "deconfliction mode" in terms of coordinating airstrikes, the general said, and not truly operating in a joint capacity.

Questions about U.S. strike

The U.S. is facing an airstrike controversy of its own after U.S. aircraft reportedly mistakenly targeted a group of of Syrian soldiers on Sept. 17. The Russian military reported that more than 60 people were killed.

The Hill reported that the U.S. point of contact for Russia wasn't immediately available when Russia called to warn the U.S. to stop the airstrikes.

"They asked to speak to their contact, and that individual wasn't next to the phone," The Hill quoted Air Force Col. J.T. Thomas, coalition spokesman, as saying. "They weren't expecting a call."

Once Russia explained that the coalition was hitting Syrian forces — not the targeted Islamic extremists — the airstrikes were stopped in "less than five minutes," The Hill quoted Thomas as saying.

At the AFA conference Tuesday, Carlisle promised the Air Force would be "very diligent" in uncovering exactly what happened.

"We'll do an investigation and determine what happened," said Carlisle said. "When something happens, we are very transparent about going in, looking at it, and sometimes we do make mistakes and sometimes we have to throw things out there where we missed something or we made a mistake."

U.S. airstrikes have also expanded out of Iraq and Syria and into other locations where extremists are operating — mainly Libya.

Carlisle declined to give the number of airstrikes the U.S. is carrying out in the country, but said the Air Force is engaging.

"We're thinking of every different way to do it and to take advantage of the assets we have in theater to conduct those strikes," he said. "The synergy of the move between the CENTCOM AOR and the African AOR allows us to swing assets in some cases."