By Barbara Starr

The U.S. military has updated its plans for a potential strike against Syria after intelligence showed that the regime has filled aerial bombs with deadly sarin gas in at least two locations near military airfields, a senior U.S. official said Friday.

A senior U.S. official confirmed the details but declined to be identified because of the sensitive nature of the information. There has been no movement to put the bombs on aircraft and no significant additional movement of chemical materials as far as the U.S. knows, he said.

The updated options are being refined daily. "The more information and intelligence you have, the more clarity you can bring to options you may decide to use," the official said. "You would expect new information like this to drive an update of options."

"We are prepared for a full range of contingencies," said Pentagon spokesman George Little.

But there is much concern, the official said. It's not clear if President Bashar al-Assad's regime is pulling back after President Obama, Secretary of State Hillary Clinton and Defense Secretary Leon Panetta issued statements condemning the action, or what al-Assad's future intentions may be.

Also: Syria's chemical weapon potential

The official also said the U.S. has all the firepower it needs in the region to conduct military action against Syria if Obama orders it. The U.S. maintains a fighter and bomber aircraft presence across the Middle East, including on board aircraft carriers. There are also warships with satellite-guided Tomahawk cruise missiles that can be programmed to hit specific targets.

But experts have said bombing a chemical weapons site or an airfield where chemical bombs are located poses significant challenges, including the possibility of dispersal of chemical agents into a civilian population. A military option could involve dropping bombs on runways to keep airplanes from taking off.

Also, communications sites could be struck to cut al-Assad's links to his troops so orders for a chemical attack cannot be issued. But U.S. officials have said they are not certain how much control al-Assad has over his military, so there is no guarantee that commanders would not act on their own.

Interrupting communications links was part of the NATO bombing strategy in Libya, but there was a sense of much tighter regime control in that campaign

Also: Assad regime has plenty of fight left

"What you have to do now is get the timely tactical intelligence to interrupt the decision cycle. That is, get between Assad and the individual who presses the button to launch that missile. That's a very big ask in the intelligence community, very difficult. But now, that's the position we're really in," CNN contributor Fran Townsend said on "Erin Burnett OutFront" on Thursday night.

The first intelligence on the chemical weapons movement in Syria came to light to the administration in the last week, when satellite imagery showed the movement of trucks and vehicles at sites where chemicals and weapons were stored. "We assume the aircraft are in close proximity to the munitions," the official said.

The U.S. also believes the order to fill the bombs was issued and carried out through the Syrian military chain of command, but it's not certain if al-Assad was directly involved. A different U.S. official told CNN several days ago that one assessment is the Syrian military may have done this to give al-Assad "options" to act as the regime came under continuing pressure from fighting near Damascus.

One reason the U.S. was certain of what it was seeing is that additional intelligence, including information provided by people, confirmed what was going on. The official would not say whether the human intelligence came from telephone intercepts, defectors or people inside Syria.