Up to 275,000 civilians in eastern Aleppo have been cut off from humanitarian aid since July, with shortages of basic commodities, including food, leading to rationing and soaring prices, UNHCR said in a statement.
The statement comes after intense fighting between the Syrian government forces and terrorists were reported in the Idlib and Aleppo provinces on Saturday and Sunday.
The Syrian army has surrounded militants in the north of Aleppo, while armed groups launched an offensive in the south.
The intense fighting has also caused the access route into western part of the city to close, effectively shutting the entire city off from aid, the statement added.
"We are seriously concerned about the grave and dangerous situation facing hundreds of thousands of civilians in Aleppo... We call upon all parties to the conflict to respect and protect the lives of civilians, medical facilities, schools, water infrastructure and humanitarian workers, and allow humanitarian organizations to carry out their duties in safety," UNHCR representative in Syria Sajjad Malik was quoted as saying in the statement.
The agency urged all parties to the conflict to observe a two-day ceasefire in order to allow the United Nations supply trapped civilians with essential aid. Syria has been mired in war since 2011, with government forces loyal to President Bashar Assad fighting numerous opposition factions and extremist groups.
On February 27, a US-Russia brokered ceasefire came into force in Syria. Terrorist groups, which maintain a heavy presence in Aleppo, are not part of the deal.
SPUTNIK/MNA