Sources: Obama has not requested review of military options for Syria

Though the White House said all options remain on the table for Syria, President Obama has not requested to see any military options for invading Syria prepared by Pentagon, two senior military officials told Fox News.

The president's lack of interest in U.S. war plans suggests it's more likely that forces will not get involved military, the officials said.

Turmoil in Syria is worsening daily, with more than 6,000 estimated dead in a year-long assault by President Bashar Assad on his own people. Recent high-profile deaths of two western journalists have added attention to the violence playing out.

One of the plans drawn up by the Pentagon in case of military action includes the destruction of Syria's air defenses and the subsequent establishment of a no-fly zone, the officials said.

On Tuesday, the State Department responded to calls from Sen. John McCain, R-Ariz., to arm the opposition, saying that option also remains on the table. Yet on Thursday, officials seemed to downplay that possibility.

Speaking in London in between a series of meetings with European and Arab leaders to discuss the Syria crisis, Secretary of State Hillary Clinton was vague.

"We will be discussing a range of options, from tightening sanctions to increasing humanitarian relief, to helping the opposition," she said.

It's unclear if the "help" Clinton mentioned will involve arms. She'll be meeting with representative from the opposition in Tunis on Friday.

White House Press Secretary Jay Carney told reporters traveling with the president on Thursday that the White House is still focused on ending this crisis with political pressure.

"Further militarization will lead to a dangerous and chaotic path," Carney said of arming opposition forces. "We'll continue to evaluate as time goes on. The fact of the matter is the aggression is being carried out by Assad and that's why we're working so hard with international partners to cease and desist."

Military plans for larger-scale military operations could be presented to the president by the Joint Chiefs of Staff on a moment's notice, but officials in the Pentagon say the president is right to be cautious. It would be a much different mission than the one in Libya last year to protect civilians and oust dictator Moammar Qaddafi.

Syria has four times the population of Libya on one-tenth the landscape. The fighting is largely urban, meaning air power would be less effective against Syrian tanks and more likely to cause civilian casualties. It's also widely believed that Syria has a larger and better-equipped military than Libya.

"Libya was a lot easier," former National Security Advisor Stephen Hadley said in an interview with Fox News. "All its population centers are on the coast. (It had) a very small and weak army that Qaddafi kept weak."

Right across the Mediterranean from Libya, Hadley added, were nearby NATO naval military bases from which to launch operations.

"So militarily it was very easy to do," Hadley said.

Hadley also pointed to concerns about arming a fragmented opposition force, which has been said to have links with al Qaeda.

National Intelligence Director James Clapper spoke about these concerns in front of a Senate panel last week.

"Another disturbing phenomenon that we've seen recently apparently is the presence of extremists who have infiltrated the opposition groups," Clapper told the Senate Armed Services Committee. "We believe that al Qaeda in Iraq is extending its reach into Syria."

Clapper also pointed to the uncertainty surrounding many chemical weapons sites in Syria that would be vulnerable should Assad lose his grip on power. Speaking on the condition of anonymity, U.S. officials told Fox News that close to 50 chemical warfare component sites exist, although Clapper made reference to only a few.

Hadley said securing chemical sites is a major issue.

"One of the concerns is if Assad were to turn those chemical weapons against his own people in order to retain power," he said. "That's another reason for really trying to accelerate his departure and turn the military, the allies and the business community against him."

Perhaps the largest distinction between Libya and Syria is Syria's lack of oil. Before the invasion of Libya, European leaders made clear they were concerned that a prolonged civil conflict would disrupt the flow of Libya's light crude oil, an asset Europe depends on.

Without that draw, the U.S. might be left on its own militarily.