Senior level Obama administration officials are now holding regular high-level meetings to discuss the ongoing situation in Syria and begin thinking about U.S. priorities in a post-Assad era, a senior U.S. official said.

"We are in the early stages of contemplating an Assad aftermath," the official said. While Syria has been a top priority for months, the official said specific concerns about the security situation in Syria have grown in recent days.

"The meetings are being convened to discuss the current situation and ensure that we are doing all we can as the crisis has worsened," the official said. "The intensity of the discussions has grown. The level of concern has increased considerably."

The administration also has stepped up its external discussions with Israel, Jordan and Turkey as the threats of spreading violence and refugees streaming across their borders has grown. There are also specific discussions with all those countries about Syria's chemical weapons stockpiles.

Syria's foreign ministry said Monday that the country has chemical weapons that it would be willing to use against foreign attackers. The admission led to strong warnings from U.S. officials, including President Barack Obama, who warned it would be a "tragic mistake."

"They should not think for one iota" about using the chemical weapons, Pentagon spokesman George Little said Monday.

And State Department spokeswoman Victoria Nuland said: "Any talk about any use of any kind of a weapon like that in this situation is horrific and chilling. The Syrian regime has a responsibility to the world, has a responsibility first and foremost to its own citizens to protect and safeguard those weapons. That kind of loose talk just speaks to the kind of regime that we're talking about."

The senior U.S. official said U.S. and allied concerns took a leap forward when extensive fighting reached Damascus last week.

"It suggested the regime might be on its last legs," the official said.

While no one can predict when, and indeed if, Assad might leave office, the uptick in fighting, the resulting violence and the increased concern about the fate of Syria's chemical weapons all have led to the increased U.S. concern and need to plan for a post- Assad era, he said.

That in turn has led to discussions about a post-Assad political framework in Syria. The official emphasized the United States is not trying to impose a new political leadership, but rather to understand which opposition leaders are out there, and their relative strengths.

To that end, the U.S. intelligence community has also sent personnel to neighboring countries to talk to opposition groups to try to determine who the United States might be able to work with, the official said.

Although the United States sees the opposition forces gaining strength, they still haven't shown they can hold ground.

Another U.S. official said, "The insurgency is clearly picking up steam and operating across larger swaths of territory. Some of the myriad groups that make up the armed opposition are talking to each other more and it looks tactical coordination is improving. The real test now is whether insurgent fighters can beat back their adversaries and hold onto key areas in the face of a counteroffensive."