The United Nations children's agency said Sunday 137 children stranded in a suburb near the Syrian capital require immediate evacuation amid a crippling regime siege in which five have reportedly died from a lack of medical care.

The Eastern Ghouta suburb, home to 400,000 residents, has been besieged since 2013 and humanitarian conditions there have deteriorated sharply amid violence that intensified since Nov. 14. The Syrian Observatory for Human Rights says at least 202 people, including 47 children, have been killed since.

The area near the capital Damascus, is technically part of a "de-escalation zone" brokered by Russia earlier this year. Cease-fires brokered by Russia have largely held elsewhere in Syria but there has been little progress toward a political solution to the conflict that has claimed nearly 400,000 lives since it began in 2011.

In its statement Sunday, UNICEF said its aid workers described seeing one of the worst health situations since the conflict began in 2011 during a rare international aid convoy to a neighborhood in the Eastern Ghouta district at the end of November.

UNICEF said 137 children, aged between 7-months to 17-years, require immediate evacuation for conditions that include kidney failure, severe malnutrition and conflict wounds.

"Children are still living through so much horror," said UNICEF Representative in Syria Fran Equiza. "The situation is getting worse day by day. The health system is crumbling and schools have now been closed for almost a month. Sick children desperately need medical evacuation, and many thousands more are being denied the chance of a normal, peaceful childhood."

UNICEF said that nearly 12 per cent of children under 5 years-old in Eastern Ghouta suffer from acute malnutrition — the highest rate ever recorded since the start of the conflict in Syria.

Since the Syrian civil war began in 2011, sieges and starvation have been used as tools of war. Placing cities under siege and cutting off access to roads, food and medical supplies have left humanitarian aid providers unable to reach the trapped populations of civilians not allowed to leave the cities.

Syria has only just begun to emerge from a devastating civil war that began in early 2011 when the Assad regime cracked down on pro-democracy protests with unexpected ferocity. Since then, hundreds of thousands of people have been killed in the fighting and more than 10 million displaced, according to claims by the U.N.