The Syrian regime on Sunday (July 17th) besieged opposition-held parts of Aleppo after severing the last supply route into eastern areas, sparking concern for thousands of civilians, AFP reported.

The UN says an estimated 300,000 people live in the opposition-controlled neighbourhoods of Aleppo, and fears are mounting that they could face starvation.

After weeks of fierce fighting, regime forces seized the strategic Castello Road and have now completely besieged the eastern neighbourhoods, said Syrian Observatory for Human Rights head Rami Abdel Rahman. The UN Office for the Coordination of Humanitarian Affairs (OCHA) confirmed the report.

The situation is particularly worrying, according to OCHA, due to the high concentration of people who have not received humanitarian supplies since July 7th.

"It is imperative that we respond to acute needs through predictable and sustained access to people in need," the report reads.

The Observatory said regime air strikes on opposition-held areas killed six civilians, including a child, and that six others, two of them children, died in opposition shelling of regime-controlled districts. At least 16 opposition fighters also were killed in Aleppo.