UN plans to reach one million Syrians with food deliveries fell short, with only 160,000 receiving assistance.
The United Nations has called for greater humanitarian access in Syria amid fears that many civilians risk starvation in besieged areas of the wartorn country.
Speaking to reporters in Geneva on Thursday, UN Special Envoy Staffan de Mistura said there "are plenty of civilians at the moment in danger of starvation" in Syria, where more than 400,000 are trapped in areas besieged by the government or armed groups across the country.
The UN also estimates that upwards of four million people are trapped in "hard-to-reach" areas.
Jan Egeland, secretary general of the Norwegian Refugee Council and special advisor to the UN envoy, told reporters plans to reach a million Syrians with humanitarian assistance have fallen short.
"Of the one million people that we have planned and have tried to reach by land in May, we've only so far reached 160,000," he said.
"Even in areas where we had full approval from the government, there have been infinite problems in actually reaching the places, and in others where we had conditional approvals, like Daraya, we haven't been able to reach the people at all."
Daraya and Moadamiyah near Damascus and al-Waer in Homs were the three places where the situation was "horrendously critical", he said.
"Children are so malnourished in these places that they will be dying if we're not able to reach them."
The UN has resorted to air drops of food to reach 110,000 people besieged by the Islamic State of Iraq and the Levant (ISIL) group in the town of Deir Az Zor, and is considering air drops to places besieged by government forces if it does not get permission to go in by land.
De Mistura said those air drops would still need government approval, but if that was denied, he expected the United States and Russia to find a way to ensure everyone could be reached.
The five-year Syrian conflict has killed more than 270,000 people in the last five years, according to the UK-based Syrian Observatory for Human Rights.
De Mistura said a new date for peace talks will be announced later on Thursday after consultations with the UN Security Council, despite the continuing violence on the ground, he told reporters in Geneva.
"There is a sense of urgency in having the talks resume, because we need to keep the momentum," de Mistura said.
"I'm not in a position now to tell you when they will be announced, but I am going be in a position of doing so after I have briefed and consulted the Security Council this afternoon."
For the talks to be credible, there needed to be improvements in the humanitarian situation and the cessation of hostilities, de Mistura said.
Time is running out before an August deadline for the peace talks, and some diplomats had expected the timetable would be even tighter because talks might not be scheduled during the Muslim holy month of Ramadan, which starts on June 6.
But de Mistura said Ramadan would "not be a factor", saying that if people were able to keep fighting during Ramadan, they could be expected to conduct peace talks.
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