Around 400 people should be urgently evacuated from the besieged Syrian town of Madaya to receive medical treatment, UN diplomats have said.
Around 35,000 people are trapped in the town and had not received supplies since October until a an aid convoy arrived on Monday.
It is "outrageous" and "illegal" that it took widespread media reports before the Syrian government regime allowed vital aid to enter the besieged down of Madaya, Justine Greening has said.
Responding to questions in the House of Commons, the International Development Secretary said the actions of Syria's president Bashar al-Assad amounted to a "breach of humanitarian law".
Up to 4.5 million people live in beseiged towns and hard-to-reach areas within the country, she said, as she revealed Assad's forces were deliberately preventing aid workers from accessing such areas.
When pressed on why the United Nations was not using its internationally-given power to enter for humanitarian purposes anyway, Ms Greening revealed 42 United Nations workers had already died in the Syrian conflict while delivering aid.
As well as protecting the workers, she said, it was essential to get the agreement of the ruling party to ensure the aid went to the right people - instead of ending up in the wrong hands.
At least 50 trucks are taking food and medical supplies to 35,000 people trapped in Madaya which had been cut off from help for months.
An aid convoy intended for starving locals in a besieged Syrian village is due to set off on Monday, amid calls for the world to do more.
Shocking images from Syria shine a light on a cruel, medieval form of torture being inflicted on citizens - starvation, writes Rageh Omaar.