In rebel-held parts of southern Damascus, activists say the streets are filled with "ghosts", Syrians wandering and begging, desperate for food and medicine that is nowhere to be found.
In February, the UN Security Council urged the government and opposition to allow aid to be delivered freely, but civilians, activists and aid workers say little has changed.
They lay much of the blame on Syria's government, for preventing UN aid deliveries through rebel-held border crossings and laying siege to opposition areas.
"The Syrian government has essentially been using a type of blackmail to not allow UN agencies to be providing the type of assistance that's really needed in opposition-held territory," said Lama Fakih, a researcher with Human Rights Watch.
UN agencies can operate only with government permission and know they could lose access to government-held areas if they work on the opposition side without regime consent, she said.
UN resolution 2139, passed with support from Syrian government allies Russia and China, demands that "all parties, in particular the Syrian authorities, promptly allow rapid, safe and unhindered humanitarian access for UN humanitarian agencies and their implementing partners."
It urges access "across conflict lines and across borders, in order to ensure that humanitarian assistance reaches people in need through the most direct routes."
Since the resolution passed, the UN has delivered aid to a rebel-held area in Aleppo city, but was forced to use a perilous path from Damascus rather than a nearby rebel-held border crossing with Turkey.
The government also allowed the UN to deliver aid through a different border crossing with Turkey that remains under regime control, with aid going to a city where regime forces maintain a presence.
Aid workers say the government's restrictions on the UN have had a knock-on effect across the entire humanitarian response effort.
"It's not just the fact that the UN can't do cross-border convoys directly to opposition-held areas, it's that all of these other parts of the machinery are not able to function as they should," said one aid worker involved in the Syria response.
"There have been endemic issues with coordination and the UN isn't funding agencies that are doing cross-border activity," she said.
"The response is bifurcated between what happens from Damascus and what happens from neighbouring countries."
There has also been little relief for the 242,000 Syrians who the UN estimates are under regime or rebel siege, around 197,000 of them trapped by government forces.
In the Palestinian Yarmuk camp in southern Damascus, more than 100 people are reported to have died because of food and medical shortages.
The UN agency for Palestinian refugees UNRWA makes sporadic aid deliveries when it gains government permission, but in the past month went two weeks without access.
"From the perspective of an aid organisation trying to work in Yarmuk, it is clear that resolution 2139 is not being implemented," UNRWA spokesman Chris Gunness told AFP.
'People dying needlessly'
In a progress report on Wednesday, UN chief Ban Ki-moon said "none of the parties to the conflict have adhered to the demands of the (Security) Council."
"People are dying needlessly every day," he said.
The resolution authorises the Security Council to take "further steps," like sanctions, in case of non-compliance, but it requires a new resolution, which Russia and China are unlikely to approve.
That leaves international and Syrian aid groups on the ground struggling to meet needs as best they can.
In southern Damascus, one activist described beggars as "ghosts" wandering the streets, their faces black with dirt because there is no running water.
"When there's a food distribution, people are so hungry they can't wait to get home to eat it," Mohammed told AFP over the Internet.
"You see grown men standing by the distribution lines and eating right there, on the street."
In southern Daraa province, another activist said local aid is dwindling as needs multiply in the fourth year of the conflict.
"At the start of the revolution, you had many people who had enough savings to help others. Now, it is no longer the case, especially as the Syrian lira is collapsing," Abu Anas said.
"The regime uses the humanitarian situation as a card to pressure people into submission," said Mohammed, the activist in Damascus.
"People say to the armed opposition: 'What can you do for us? Can you bring us food?'"