President Barack Obama met Syrian opposition leader Ahmad Jarba in a show of support for moderate, embattled foes of President Bashar al-Assad.
Both sides said the meeting was productive and marked an important step in the evolving relationship between the United States and the opposition.
It took place however as the Obama administration again voiced concerns that any deadly aid that was provided at the request of rebels in Syria could end up in the hands of extremists.
Obama dropped by a meeting between Jarba, president of the Syrian National Coalition, and his national security advisor Susan Rice.
The White House said Obama and Rice condemned "the Assad regime’s deliberate targeting of Syrian civilians through aerial bombardments -- including the use of barrel bombs -- and the denial of food and humanitarian assistance to civilians located in areas under siege by the regime."
- Thanks for aid -
Jarba, according to a White House statement, thanked Obama for a total of $287 million in US aid to opposition forces and noted the US role as the largest humanitarian donor to Syrian refugees with a total aid grant of $1.7 billion.
But there was no mention in the statement of Jarba's previous plea to the administration for anti-aircraft weapons to combat the barrel bombings unleashed by Assad's forces.
US officials privately acknowledged he made the request in talks with Secretary of State John Kerry at the State Department last week, but they refused to be drawn on the response.
Signup to our newsletter and follow us on Facebook and Twitter!
Washington is worried that such weapons could eventually end up in the hands of groups hostile to the United States or its allies and could even pose a threat to commercial aircraft.
White House spokesman Jay Carney said earlier that Washington had worked hard to "ensure that the aid that we are providing the opposition is getting into the hands of the moderate opposition and not falling into the wrong hands."
"This is something that has been a concern and an issue, obviously, since the beginning of the conflict there, but it is one that we take very seriously."
Officials say the non-lethal assistance that is being provided includes communications equipment, body armor and night-vision goggles -- but declined to give a detailed inventory of the aid.
The Syrian National Coalition described the talks as "encouraging and productive" and a milestone on the road to a closer partnership between the Syrian people and the United States aimed at ending the suffering in the country and producing a transition to democracy.
A coalition statement also hinted at the need for more robust military help for opposition groups.
"The opposition delegation discussed the need to empower the Syrian people to defend themselves against the war crimes committed by the regime daily and the need for more pressure against Assad to accept a political solution," the statement said.
Jarba's visit came at an inauspicious time for opponents of Assad, after rebels pulled out of the battleground city of Homs and UN and Arab League mediator Lakhdar Brahimi resigned after failing to broker a political solution to the war which has claimed 150,000 lives.
Speaking after meeting Kerry last week, Jarba thanked Kerry for Washington's support "for the struggle of the Syrian people, for freedom and democracy, and also to lift the injustice and fight oppression and dictatorship that Bashar al-Assad is engaging in."
But he stressed the Syrian people were looking for more concrete support from "the superpower and country that plays a leading role in the world."
Washington has many times warned that Assad has lost legitimacy and must go, but Obama has been wary of embroiling the United States in another foreign conflict, after spending years pulling US troops out of Afghanistan and Iraq.