US State Department spokesman Mark Toner Toner acknowledged Wednesday that the situation hadn't been ideal.
"We've seen violations by both sides", he said, adding, "we're continuing to monitor this very closely".
The number of deaths recorded since the beginning of the conflict in March 2011 recently rose above 300,000, according to the Syrian Observatory for Human Rights, a UK-based monitoring group. He says he has also been in touch with the Americans to get Syrian armed groups to cooperate.
The guns are silent, the killing has stopped but there was still no relief for tens of thousands of desperate Syrians on Wednesday.
However, some 20 trucks carrying U.N aid and destined for rebel-held eastern Aleppo remained in the customs area on the border with Turkey on Wednesday "because of lack of de facto assurances of safe passage by all parties", Jens Laerke, deputy spokesman for the United Nations office for the Coordination of Humanitarian Affairs, told The Associated Press in an email.
A day earlier, the government said rebels had targeted the Castello road, the only remaining artery by which aid reaches the eastern, rebel section of Aleppo.
The aid arrived Wednesday, the third day of the Muslim Eid al-Adha holiday. This is something promising. "Based on what we're hearing from the ground, it's not likely to happen today".
"The convoy is ready and will move as soon as conditions allow".
The White House is blaming Syrian President Bashar Assad's government for preventing humanitarian aid from entering high-need areas of Syria.
"That is what makes a difference for the people, apart from seeing no more bombs or mortar shelling taking place", he said of the aid deliveries that are supposed to be part of the truce deal.
Russia's military announced Thursday evening that Syrian government forces had begun withdrawing from the route to Aleppo, though the Pentagon said it had no indication of a withdrawal.
East Aleppo, where around 250,000 civilians are besieged by government forces, is a major concern for humanitarian organisations.
"The regime is still insisting that the aid deliveries go through it", Sabra said in a telephone interview.
Ban said the United Nations hopes to take advantage of the cease-fire deal reached over the weekend after marathon negotiations between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov to "immediately deliver vital humanitarian assistance to Aleppo and other besieged and hard-to-reach locations".
Khandakani is a volunteer at a medical center in eastern Aleppo.
Earlier on Thursday, activists said the cease-fire was still holding despite some violations.
Russia's Defense Ministry said Thursday the United States was not fulfilling its obligations under the Syrian ceasefire agreement, as Moscow and Washington pointed fingers at each other for violating what had appeared to be a peaceful lull in fighting. On Tuesday Jabhat Fateh al-Sham threatened to form an alliance with USA -backed and other rebel factions, which would vastly complicate Russian and US efforts to target the group without also endangering those covered by the agreement.
Russian Federation has urged Syrian rebels to separate themselves from "terrorists" so that the ceasefire can hold.
A crucial part of the deal calls on non-extremist rebels to break ranks with Jabhat Fatah Al Sham ahead of joint US-Russian operations against the group.
The deal, reached on Saturday, would entail US military cooperation with Russian Federation to target the Islamic State in Iraq and Syria (ISIS) and other terrorists in Syria, if a seven-day temporary ceasefire holds.
Russian Federation and American officials have said the agreement is meant to set the stage for peace talks to resolve the Syrian war, now in its sixth year.
"This ceasefire was brought about by outside powers - it was brought about by the United States and Russian Federation, and then basically the warring parties here were told that they are to abide by the ceasefire, so its very, very fragile", Pleitgen said.
Some 4.8 million Syrians have been forced to leave the country, and 6.5 million are internally displaced, making Syria the largest displacement crisis globally.