Besieged civilians in the opposition-held areas waited desperately for aid on Wednesday as relief convoys remained on hold despite a significant drop in violence under a ceasefire brokered by Washington and Moscow. The U.N. envoy Staffan de Mistura hailed a "significant drop in violence" over the first 24 hours of the cease-fire, but said no U.N. aid trucks have yet moved across the Turkish border into Syria. He said U.N. officials are awaiting assurances that the drivers will be "unhindered and untouched." He said aid for rebel-held eastern Aleppo is a top priority, and that a key concern about the overall cease-fire is whether sporadic "incidents" snowball to threaten the deal.

Dozens of residents in the opposition-held part of Aleppo protested against the United Nations and demanded the lifting of the Assad's siege of the area, which is home to some 250,000 people.

As the truce largely holds, the Pentagon said Tuesday it launched various strikes on DAESH in Syria over the past several days, including hits on some targets that "may have resulted in civilian casualties." The incidents took place September 7, September 10 and September 12, according to a statement from CENTCOM. It did not give a number of dead or injured.

The U.S. Secretary of State John Kerry on Wednesday sought to diffuse criticism of a U.S.-Russian ceasefire agreement on Syria arguing that without it violence would increase significantly with many more Syrians slaughtered or forced to flee the war-torn country.

The deal struck between Kerry and Russian Foreign Minister Sergei Lavrov in Geneva on Friday agreed to a seven-day period of reduced violence and increased humanitarian aid deliveries.

The deal also crafted by the U.S. and Russia to halt the Syrian civil war is rife with legal and liability questions that are fueling skepticism from both sides about military cooperation between the two powers. The first hurdle is that the U.S. Congress has enacted a law prohibiting any military cooperation with Moscow in the wake of Russia's annexation of the Crimea region of Ukraine. That means the deal that the U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov agreed to last week in Geneva first needs a waiver from a skeptical Defense Secretary Ash Carter to be legal.

Another nagging question revolves around whether America could be held responsible if a Russian airstrike approved by the U.S. as part of the military cooperation at the heart of the deal, kills civilians. Military and defense leaders question whether Russia will be able to force the Assad regime to uphold the cease-fire.

If the cease-fire holds for seven days and humanitarian deliveries continue, the U.S. would begin discussions with Russia on the establishment of a joint implementation cell. If the cease-fire is violated, the seven-day time period resets, State Department spokesman Mark Toner said.

U.S. officials said the cooperation will not begin immediately after the seven days. They said it could be shut down quickly if humanitarian aid stops getting through or if the Assad regime violates the cease-fire. The Pentagon's top leaders insisted on the seven-day waiting period, largely due to deep skepticism about Russia. Toner said he had no estimate on how long it would take to set up the coordination center, but said discussions have been going on for several months, so he didn't believe it would "be a matter of weeks."

Russia is not part of the U.S.-led coalition targeting DAESH in Iraq and Syria, and the U.S. does not have a history of sharing information with Moscow. U.S. officials expressed concerns that Moscow might continue to target U.S.-allied opposition forces. They also worry that many of the Russian airstrikes do not involve precision-guided weapons. Moscow has predominantly used so-called dumb bombs in Syria, largely targeting opposition forces and backing Assad's forces.