Syria's warring parties "needlessly hindered" life-saving aid after the disastrous earthquake in February, UN investigators have reported.
There were "multiple reports" of aid being diverted, extorted or disappearing due to corruption, a human rights commission said.
The pro-government Syrian army allegedly blocked supplies to mainly Kurdish, earthquake-affected neighbourhoods in Aleppo.
President Bashar Al Assad's government and other parties "continued shelling targets in the earthquake-affected area", said the commission's twice-a-year report on the conflict.
The 7.8-magnitude earthquake on February 6 killed at least 58,000 people across southern Turkey and north-western Syria. Schools, hospitals and homes were destroyed in an area where many people were already in urgent need.
The humanitarian response was tangled up by the conflict in Syria, where there are few ways to deliver help to opposition-held territory. Western sanctions on Syria were eased to facilitate aid, but a Russian veto in July blocked the UN from keeping a key border crossing open.
Unveiling the latest report in Geneva, commission chair Paulo Pinheiro said investigators were "depressed and sad" that the UN's call for a post-earthquake ceasefire was not heeded.
It was "appalling that the victims suffer from the earthquakes, but they continue suffering from the armed conflict", Mr Pinheiro said.
Fellow inspector Lynn Welchman said the horse-trading over aid was "a stark reminder of how hostilities, politicisation and fragmentation in Syria harm civilians and deprive them of much-needed assistance".
“Is it too much to ask that the parties and the international community ensure that cross-border humanitarian assistance can continue at the necessary scale and in a principled, needs-based and sustainable manner?", she said.
The 34-page report said Syria's government placed "severe bureaucratic burdens" on aid groups trying to help affected people.
It described the the Syrian army's "obstruction of supplies to the earthquake-impacted, predominantly Kurdish, enclaves of Shaykh Maqsud and Ashrafiyah" in the north of Aleppo.
Opposition forces also obstructed aid, according to the report. It said various authorities failed to allow aid, rescue teams or equipment "through any available route in the vital first week after the earthquake".
The commission "received multiple reports of aid diversion, extortion and corruption, and documented aid obstruction and interference in aid delivery in the immediate aftermath of the earthquake".
"Political or ideological differences are not valid reasons to withhold consent for allowing impartial humanitarian assistance for those in need," the report said.
It said the Syrian army and militant group Hay’at Tahrir al-Sham violated international humanitarian law by "refusing to allow urgently required impartial humanitarian aid".
Russia's veto put a stop to UN operations at the Bab Al Hawa crossing with Turkey, one of the last remaining openings to opposition-held Syria.
The UN said a Syrian offer to keep the crossing open came with "unworkable conditions". However, it said last month that terms had been agreed with Damascus for six months.
Investigators said these "ad hoc arrangements" would endanger much-needed support.
