The UN heads expressed dismay that a similar call of "Enough, we said, enough!" was issued a year earlier with no response.
With the war in its fourth year, the officials noted that 9.3 million people have been affected by the civil war, most of whom lack access to medical care and clean water -- amongst other necessities -- and "the innocent civilians of Syria seem to be surviving on sheer courage."
The UN officials acknowledged "we are doing all we can to save lives and alleviate suffering ... But we know that what we can do is not sufficient."
In order to reach more people, the UN humanitarian heads called on "all parties" to undertake the following actions:
-- Enable unconditional humanitarian access to all people in need, using all available routes either across lines inside Syria or across its borders.
-- Lift the sieges on civilians currently being imposed by all sides, such as those now sealing off parts of Aleppo, the Old City of Homs, Yarmouk, East Ghouta, Moadhamieh, Nubl and Zahra.
-- End the indiscriminate bombing and shelling of civilians by the Government and opposition groups and stop all other violations of international humanitarian law.
The statement was signed by UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Valerie Amos, UNICEF Executive Director Anthony Lake, UN High Commissioner for Refugees António Guterres, World Food Programme Executive Director Ertharin Cousin, and World Health Organization Director-General Dr. Margaret Chan.