(CNN) -- Aircraft including long-range bombers may be used in any eventual strike on Syria, but "that does not fundamentally change the parameters of the mission," a U.S. official said.
Another official from the Defense Department said the White House has been calling the Pentagon almost every day asking questions about U.S. options in Syria and the feasibility of different plans.
"They're not the experts on this, we are. So it's our job to lay out what it would take to accomplish X or Y," the defense official said.
The questions from the White House involve escalating the scope of the mission, but "in increments -- nothing that's out of line with the original plans. From the start, we have always been developing a range of options, depending on what they ultimately wanted to do," the defense official said.
The first official said planners have had what he described as "incremental inquiries into what we might apply, due to how things have been developing on the ground," but added that no final decision has been made on which assets to deploy and that a decision could still be a ways off.
"I wouldn't get out ahead of anything here," the official told CNN.
"You want to match the military effort to the target sets. Those target sets have changed, but they're probably going to continue to change even more," he said.
The official characterized the bombers only as options and pushed back on any notion of U.S. pilots flying over Syrian airspace.
"You can employ stand-off weapons from an aircraft, just as easily as from a ship or submarine. Aerial assets can be used from a distance," he said.
The official was responding to a report from ABC News' Jonathan Karl, who is traveling with President Barack Obama in Russia, that said the U.S. attack plan for Syria could potentially include missiles fired from B-2 and B-52 bombers flying from the United States.
The Wall Street Journal, meanwhile, has reported that the Pentagon was preparing to employ greater firepower to reach shifting military targets. The revised options under development include the use of Air Force bombers to supplement U.S. destroyers in the Mediterranean, the newspaper said.
U.S. long-range bombers such as the B-1, B-2 and B-52 are equipped with joint air-to-surface missiles, designed to destroy both mobile and fixed targets. The missiles' primary advantage is that they allow pilots to operate outside the lethal range of most hostile air defense systems.
The United States has B-1 bombers stationed at Al Udeid Air Base in Qatar, which also operates as a forward headquarters for U.S. Central Command.