The humanitarian situation in Syria is worsening and the number of people needing urgent help has reached 10.8 million - almost half of Syria's population of 22 million, said United Nations Secretary-General Ban Ki-moon.
Ban's monthly report to the UN Security Council said the current estimate of 3.5 million people living in areas that are difficult or impossible for humanitarian workers to reach is also likely to have increased to 4.7 million people.
The UN chief painted a grim picture of a country gripped by severe levels of violence, including the intensified use of barrel bombs by government forces against civilian areas and suicide attacks, reported executions and other acts of terrorism by extremist groups. As a result, Ban said, the number of people in need has increased by 17 per cent - from 9.3 million to 10.8 million.
Ban said the rules that govern the conduct of war were being "flagrantly violated every day" and that efforts to expand humanitarian assistance "have been met with continued delays and obstruction".
All UN aid must go through Damascus - a practice UN humanitarian chief Valerie Amos has criticised.
New procedures sealing government trucks delivering aid which were introduced in April resulted in fewer people being reached with aid in May, he said, and additional clearance requirements introduced by the Government have further undermined access to people in desperate need of assistance.
By June 9, only 12 per cent of the 4.25 million people the UN World Food Programme planned to provide with food had been reached compared to 26 per cent at the same time in April, Ban said.
Ban decried the Government's obstruction of the delivery of medicine and medical supplies, saying "it is inhumane and unlawful" that these potentially life-saving items continue to be removed from World Health Organisation convoys entering opposition-controlled areas.
As a result, he said, opposition-controlled areas received only 25 per cent of the quantities distributed in the first three months of this year.
"Tens of thousands of civilians are being arbitrarily denied urgent and lifesaving medical care" which Ban called "a deliberate tactic of war aimed at denying help and support to those most in need."
Ban said Physicians for Human Rights reported that 29 medical personnel were killed in May, "the highest number in a month since the start of the conflict". That took the total recorded deaths of medical personnel in the war to 502.
Ban said the UN was unable to provide an assessment of the presence and activities of foreign fighters. But he said the recent advance of the al-Qaeda-inspired Islamic State of Iraq and the Levant is expected to have an impact on Syria's eastern regions "and may strengthen the presence of extremist groups in (Isis) controlled areas of Syria."
Key council members have been negotiating a new humanitarian resolution that would authorise the delivery of aid into Syria through four border crossings without approval from President Bashar al-Assad's Government. But Western nations, who back Syria's opposition, and the Syrian Government's closest ally Russia are reportedly still at odds over its provisions.