The heads of five UN agencies on Wednesday made an impassioned call to both sides in Syria's conflict to allow aid deliveries countrywide, end siege warfare and halt indiscriminate attacks on civilians.
"The war escalates in many areas. The humanitarian situation deteriorates day after day," the leaders of the UN humanitarian aid office and its children's, refugee, food and health divisions said in a joint statement.
"For the civilians remaining in the cities of Aleppo and the Old City of Homs, as well as other parts of the country experiencing heavy fighting, the worst days seem yet to come," they warned.
In Aleppo alone, at least one million people are now in need of urgent humanitarian assistance, but the road linking the northern city to Damascus has often been cut by the warring sides.
"All too often, humanitarian access to those in need is being denied by all sides. Aerial bombardment, rockets, mortars and other indiscriminate attacks slaughter innocent men, women, and children," the aid chiefs said.
In Aleppo, there are now only 40 doctors for a population of 2.5 million, where once there were more than 2,000.
Signup to our newsletter and follow us on Facebook and Twitter!
And across Syria, more than 9.3 million people are now affected by the conflict which erupted in March 2011, they said.
"With a third of the nation's water treatment plants no longer functioning, with 60 per cent of health centres destroyed, and with some 3.5 million people living in areas under siege or unable to be reached with humanitarian assistance, the innocent civilians of Syria seem to be surviving on sheer courage," they said.
Aid agencies are doing all they can to save lives and alleviate suffering, despite the huge risks staff face operating in a war zone, the five UN officials said.
"But we know that what we can do is not sufficient. Not nearly so. If we are to do more, to reach and help more people, those engaged in this horrific conflict, and those with influence over them, must do more," they insisted.
They set down three demands.
They called on all in involved in the conflict to "enable unconditional humanitarian access to all people in need, using all available routes either across lines inside Syria or across its borders."
Both sides must also lift the sieges imposed on civilians, they said, citing areas including Aleppo, the Old City of Homs and Yarmuk as well as Eastern Ghouta, Moadamiyet al-Sham, Nubl and Zahra.
They also called for an end to the "indiscriminate bombing and shelling of civilians by the government and opposition groups" and a halt to "all other violations of international humanitarian law".