Washington (CNN) -- U.S. lawmakers expressed frustration with Obama administration handling of arms shipments to the Syrian rebels amid reports military aid has been held up by key members of Congress.
No one spoke openly about the shipments, but plenty of lawmakers acknowledged concerns.
A source with knowledge of congressional briefings on the matter said they didn't go well and there was a lot of frustration about the lack of an explanation from the administration about strategy and how it was vetting groups to receive aid.
Asked on Tuesday why assistance was not being sent to Syria, White House spokesman Jay Carney would only say the White House was engaged in discussions with Congress and referred the question to the appropriate congressional committees.
"I think that we're going to work with Congress as the president noted when he announced the expansion of our assistance to the Supreme Military Council -- the president said that we would consult with Congress, and that's what we're doing," Carney said.
The administration said in June that Syrian government troops had crossed a "red line" by using chemical weapons against rebel forces, prompting it to increase what so far had been non-lethal aid to the opposition.
The administration plan calls for sending small arms, ammunition and potentially anti-tank weapons to the rebels, officials familiar with the matter told CNN.
But lawmakers and others have raised concerns that any U.S.-supplied weapons could fall into the hands of militants who are said to comprise elements of rebels battling forces loyal to Syrian President Bashar al-Assad in a bloody civil war.
Sen. Susan Collins, a Maine Republican and a member of the Intelligence Committee, said she couldn't share a lot because the briefings were classified.
"All I can say is that I have concerns that we could end up providing weapons that prolong but do not decide the conflict," she said.
"I don't think the administration has really had a plan," she said.
Rep. Dutch Ruppersberger, the top Democrat on the House Intelligence Committee, declined to confirm his committee is holding up the aid.
But he acknowledged that he and the committee's chairman, Republican Mike Rogers of Michigan, have "some issues" they are talking to the administration about.
But he expects them to be resolved.
"Rogers and I have been working very closely, as has the committee, with the administration -- we're trying to resolve our issues," the Maryland Democrat said.
"But we want to make sure whatever we do we do it right. We want to make sure whatever we do -- if we supply any weapons -- that it does not get into the hands of an al Qaeda who are our enemies," Ruppersberger said.
Asked to elaborate on what issues were being discussed with the administration, Ruppersberger would only say they want more on "the plan -- what we're going to do. Are we going to provide training? How much is our involvement going to be? That kind of thing."
Senate Intelligence Committee Chairman Dianne Feinstein also said she had concerns but noted the administration had taken steps to ally them.
"Obviously, one always has concerns. But I think those concerns are being met," said Feinstein, a California Democrat.
She nodded affirmatively when asked if it was the administration addressing her concerns.
Joint Chiefs Chairman Gen. Martin Dempsey has said the United States faces a long-term issue in Syria.
Dempsey said in an interview aired Sunday on CNN's "State of the Union" that the conflict is entwined in a regional issue that is now spilling over into both Lebanon and Iraq, and those underlying causes will persist for a decade.
"It is related -- not exclusively -- but related to a competition at best and a conflict at worse between the Sunni and Shia sects of Islam, and it's been hijacked at some level on both sides by extremists -- al Qaeda on one side and Lebanese Hezbollah and others on the other side," he said.
Syria's civil war began in early 2011 when al-Assad's regime turned police and troops on anti-government demonstrations.
The crackdown mushroomed into a conflict that has left more than more than 90,000 dead, according to the United Nations.
CNN's Ted Barrett, Elise Labott, Matt Smith and Deirdre Walsh contributed to this report