Key GOP lawmaker: 'We don't have a lot of good options' on Syria

"There's been talk about helping provide some assistance to the resistance movement inside Syria. On the other hand, they are not a organized group," Thornberry aid on C-SPAN's "Washington Journal" Wednesday. "You also have to be very careful in that area about the domino effect."

Thornberry said he is concerned that destabilization within Syria could have a ripple effect in Lebanon and Jordan and cause a flow of refugees into Turkey or Iraq.

"I don't think any of us should be cavalier about saying, 'Yeah, we need to go get that guy,' " Thornberry said, referencing Syrian President Bashar al-Assad's continued government crackdown and killing of civilians.

The Pentagon is looking into possible military options in the region, CNN reported on Wednesday, though the Obama administration remains focused on diplomatic solutions.

U.S. officials described the Pentagon review as a routine planning exercise to give President Obama options if he wants them, according to CNN.

The Texas congressman took a more reserved stance than some of his GOP colleagues on the use of military force, telling C-SPAN that it's not yet "clear" to him whether the United States should intervene.

"Its not clear to me; we need to be a little more clear than I think we are now what difference our military involvement would mean and what sort of military involvement we're willing to do," he said.

Several lawmakers began calling this week for military alternatives to be put on the table.

Sen. John McCainJohn Sidney McCainManchin, Donnelly back Pompeo This week: Senate barrels toward showdown over Pompeo Romney forced into GOP primary for Utah Senate nomination MORE (R-Ariz.), ranking member of the Senate Armed Services Committee, told reporters Tuesday that “we should start considering all options, including arming the opposition. The blood-letting has got to stop."

Thornberry said the regional complexities and potential domino effect make the situation in Syria "infinitely more complex" than in Libya, where U.S. and NATO military involvement helped topple the Moammar Gadhafi regime last year.

"The Syrian regime is even more difficult and obviously incredibly brutal, willing to kill however many people it takes in order to hold on to power and we know have chemical, biological weapons, so there are some different dimensions here that I think we ought to be careful about," he added.