(CNN) -- The United States is not interested in providing weapons to opposition forces in Syria until it has a better picture of what those forces are, the top U.S. military officer said in an interview aired Sunday.
"I think it's premature to take a decision to arm the opposition movement in Syria, because I would challenge anyone to clearly identify for me the opposition movement in Syria at this point," Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, told CNN's "Fareed Zakaria GPS."
More than 50 prominent U.S. conservatives signed an open letter last week urging the Obama administration to "take immediate action" against the Syrian regime, including "self-defense aid" to an armed opposition led by defected government troops. Among the signatories were some of the leading voices in support of the 2003 invasion of Iraq, as well as the former head of the U.S.-led occupation government there.
And Sen. Joe Lieberman told CNN last week that a "coalition of the willing" should assist Syria's opposition forces since Syrian allies Russia and China vetoed action at the United Nations. Lieberman, a Democrat-turned-independent who was also a leading Iraq hawk, said the United States and its allies could provide the rebels with medical aid, communications and ultimately, weapons.
But Dempsey, an Army general who served two tours of duty in Iraq, warned that Syria is "an arena right now for all of the various interests to play out." Those interests include neighbors such as NATO ally Turkey; the region's Sunni and Shiite Muslim powers, Saudi Arabia and Iran, which is Syria's leading ally; and the al Qaeda terrorist network, which has shown signs of interest in the conflict, he said.
"There's a number of players, all of whom are trying to reinforce their particular side of this issue. And until we're a lot clearer about, you know, who they are and what they are, I think it would be premature to talk about arming them," Dempsey said.
Syria's uprising began amid the "Arab Spring" demonstrations in March 2011, when longtime autocrats fell in Tunisia and Egypt and others found themselves battling popular revolts. Syria's government responded by unleashing police and troops on opposition protests.
The United Nations says more than 5,000 people have been killed in the crackdown. Syrian opposition groups put the figure at more than 7,000, with government troops shelling the flashpoint city of Homs for two consecutive weeks, while President Bashar al-Assad's government says it is battling "terrorists."
Supporters of intervention point to the results in Libya, where U.S. and NATO airstrikes helped an armed rebellion topple longtime strongman Moammar Gadhafi last August. But Dempsey said Syria is "a very different challenge," since the opposition controls very little territory and Syria has a more capable military than did Libya.
"I think intervening in Syria would be very difficult," Dempsey said.
The United States, the European Union, the Arab League and Turkey have initiated a range of sanctions against Syria. The Obama administration has said al-Assad has lost his legitimacy to rule, and it is working on ways to bolster the opposition through a coalition of Western and Arab states called the "Friends of Syria."
But State Department spokeswoman Victoria Nuland said Friday, "We don't think further militarizing the situation is going to bring peace and stability and a democratic transition to the people of Syria."