"The good news is that our people on the ground confirmed that the cessation of hostilities is largely holding, the killing has been greatly reduced... Attacks on schools, attacks on hospitals have stopped,"
said Jan Egeland, the adviser to the special UN envoy to Syria.
"The bad news is that we are not using this window of opportunity so far to reach all of these places with humanitarian assistance."
A convoy of 20 trucks filled with aid and medical supplies for Aleppo has been waiting for authorization for more than 48 hours, according to Egeland.
Drivers will be blocked from reaching affected areas if the proper permits are not presented, he said.
'Well-fed grown men, please stop'
Egeland reiterated the call for quick action in allowing humanitarian access.
"Well-fed grown men, please stop putting political, bureaucratic, and procedural roadblocks [before] brave humanitarian workers that are willing to go to serve women, children, wounded civilians in besieged areas," he said.
In addition to rebel-controlled eastern Aleppo, UN convoys with the right permits are willing to go to Moadameya, Al-Waer, Talbiseh, Douma and other besieged areas, according to Egeland.
As officials work to get access for aid convoys, the two main players in the ceasefire deal accused each other of not meeting expectations.
Russia's Defense Ministry said Thursday that the United States was not fulfilling its obligations under the ceasefire agreement.
Washington pointed the finger right back at Moscow, accusing it of not holding up its end of the deal.
Russia said US-led "moderate opposition forces" had increased attacks on residential neighborhoods, claiming at the end of the deal's third day that "only the Syrian army observes silence mode."
A US official told CNN Friday that until the humanitarian aid begins to flow, the Pentagon will not consider the Russians or the regime to be in compliance with the ceasefire agreement.
Under the terms of the deal, if the peace holds for seven days, Russia and the United States will establish a Joint Implementation Center -- which will be located in Geneva -- for cooperation on military operations in Syria targeting terror groups.
The Syrian government then would be barred from conducting air operations in those areas.
According to the official, the Pentagon is working on initial planning for how the center would operate, but is not going to make extensive details public until, and unless, the Russians and regime come into compliance
Meanwhile, Russian Defense Ministry spokesman Igor Konashenkov says attempts made by the US to show the world that the "moderate opposition" in Syria is controllable have yet to prove successful so far.
"Although the regime of cessation of hostilities envisaged by the Russian-US agreement is in its fourth day the question of whether the 'moderate opposition' is capable of complying with it in principle remains open," Konashenkov told reporters Friday.
"All attempts by our US partners to show to the world the opposition it has been sponsoring is controllable to some extent have been futile. Although the ceasefire agreement is bilateral, only one party implements it in reality.
"There is every sign our American partners have failed to find in Aleppo any 'moderate opposition' groups, whose good organization and controllability has been so much talked about."
At least 23 people died in airstrikes in Syria on Thursday.
The Syrian Observatory for Human Rights said it was unclear which side was behind the airstrikes in the eastern province of Deir Ezzor, an area not included in the ceasefire.
One of the targets was a school used as a shelter for families displaced by the fighting, according to the rights group.
The town targeted in the raids, Al-Mayadin, is controlled by ISIS. The ceasefire does not apply to areas held by the group and the airstrikes would not be considered a violation of the deal.
The ceasefire deal went into effect Monday and calls for a halt to the violence between the Syrian regime and rebel forces, but it does not cover militant groups considered terrorists, such as ISIS and Jabhat Fateh al-Sham
, formerly known as al Nusra Front.
But convoys still haven't been able to get humanitarian aid to those in need, and such delivery is an important way to judge if a ceasefire is successful.
Syria has said aid can only be delivered to Aleppo if it is coordinated through the government and United Nations.
Nevertheless, the ceasefire appears to have offered a respite in the civil war that's killed an estimated 430,000 people since 2011 and touched off an international refugee crisis.