Another 16 people have starved to death in the besieged Syrian town of Madaya since UN aid convoys reached it earlier this month, according to charity Medecins Sans Frontieres.
The charity says there are also 33 people in danger of dying.
Brice de la Vingne, MSF operations director, said the situation was "totally unacceptable" when people "should have been evacuated weeks ago".
MSF previously said 30 people died of starvation in the town late last year.
Earlier in January, two emergency convoys of food and aid supplies were delivered to Madaya, where up to 40,000 people are believed to be trapped in appalling conditions.
The report comes as talks on ending the Syrian conflict take place in Geneva.
Negotiators representing Syria's main opposition groups are expected to arrive later on Saturday, after earlier boycotting the launch of the peace talks. Aid deliveries to besieged towns is a key demand from opposition groups.
The UN says some 400,000 people are trapped and in need of emergency assistance in 15 locations in Syria as as part of sieges imposed by the Syrian government-led coalition, as well as by opposition groups.
Madaya, in the mountains 25km (15 miles) north-west of Damascus, has been besieged for six months by government forces and their allies in Lebanon's Hezbollah movement.
Humanitarian agencies have called for hundreds of people to be evacuated immediately for medical treatment.
However, MSF said residents were continuing to die as government coalition forces prevented sick people leaving, and supplies of food and medical supplies getting in.
March 2015: Foah and Kefraya in Idlib province are besieged by rebel groups and the al-Qaeda-affiliated al-Nusra Front, with an estimated 12,500 trapped.
July 2015: Madaya, near Damascus, is besieged by government forces and their allies in Lebanon's Shia Islamist Hezbollah movement.
September 2015: The situation in Foah and Kefraya worsens after the fall of a nearby government air base, where helicopters had been able to land with food supplies. Reports emerge of people eating grass to survive.
October 2015: UN delivers one month's supply of food rations for 20,000 people in Madaya.
December 2015: Dozens of wounded civilians and fighters evacuated from Foah, Kefraya, Zabadani and Madaya. Reports begin to emerge of people starving in Madaya.
January 2016: UN says it has received credible reports of people dying of starvation in Madaya
"It is totally unacceptable that people continue to die from starvation, and that critical medical cases remain in the town when they should have been evacuated weeks ago," said MSF's director of operations.
The 16 recent deaths were reported by health workers supported by MSF in the town. No doctors are present to help, the organisation said.
Previously MSF said almost 30 people had died of starvation at a clinic in Madaya between 1 December and early January.
However, Hezbollah denies there have been any deaths in the town and accuses rebel leaders of preventing people leaving.
More than 40 lorries delivered aid to Madaya earlier this month - including rice, vegetable oil, flour, sugar and salt - for the first time since October.
The UN hopes to deliver further aid to Madaya as well as two northern towns besieged by Sunni rebels, Foah and Kefraya.
What's happening in Syria?
More than 250,000 Syrians have lost their lives in almost five years of conflict, which began with anti-government protests before escalating into a brutal civil war. More than 11 million others have been forced from their homes as forces loyal to President Bashar al-Assad and rebels opposed to his rule battle each other - as well as jihadist militants from Islamic State.
Why are civilians under siege?
All parties to the conflict are using siege warfare, encircling populated areas, preventing civilians from leaving and blocking humanitarian access in an attempt to force opponents to surrender. Shortages of food, water, medicine, electricity and fuel have led to malnutrition and deaths among vulnerable groups.
Where are the sieges?
Government forces are besieging various locations in the eastern Ghouta area, outside Damascus, as well as the capital's western suburb of Darayya and the nearby mountain towns of Zabadani and Madaya. Rebel forces have encircled the villages of Foah and Kefraya in the northern province of Idlib, while IS militants are besieging government-held areas in the eastern city of Deir al-Zour.