Syrian troops besiege rebel-held parts of Aleppo

FILE - In this Aug. 5, 2012 file photo, a Syrian man holds bullets he picked from the wall of a damaged house in the town of Atareb, on the outskirts of Aleppo, Syria, Sunday, Aug. 5, 2012. Syrian opposition activists said Sunday, July 17, 2016 that government forces and their allies have closed the only road leading into and out of rebel-held parts of the northern city of Aleppo, besieging hundreds of thousands of people. The Britain-based Syrian Observatory for Human Rights says government forces and members of Lebanon’s Hezbollah group reached the Castello road Sunday, closing it and raising fears of a humanitarian crisis. (AP Photo/Khalil Hamra, File) (The Associated Press)

FILE -- In this Dec. 14, 2012 file photo, a Syrian woman chants slogans against President Basar Assad during a weekly demonstration in Aleppo, Syria. Syrian opposition activists said Sunday, July 17, 2016 that government forces and their allies have closed the only road leading into and out of rebel-held parts of the northern city of Aleppo, besieging hundreds of thousands of people. The Britain-based Syrian Observatory for Human Rights says government forces and members of Lebanon’s Hezbollah group reached the Castello road Sunday, closing it and raising fears of a humanitarian crisis. (AP Photo/Manu Brabo, File) (The Associated Press)

FLE -- In this Nov. 15, 2012 file photo, a Syrian rebel reads Quran during clashes with government forces in Aleppo, Syria. Syrian opposition activists said Sunday, July 17, 2016 that government forces and their allies have closed the only road leading into and out of rebel-held parts of the northern city of Aleppo, besieging hundreds of thousands of people. The Britain-based Syrian Observatory for Human Rights says government forces and members of Lebanon’s Hezbollah group reached the Castello road Sunday, closing it and raising fears of a humanitarian crisis. (AP Photo/ Khalil Hamra, File) (The Associated Press)

Syrian opposition activists say government forces and their allies have closed the only road leading into and out of rebel-held parts of the northern city of Aleppo, besieging hundreds of thousands of people.

The Britain-based Syrian Observatory for Human Rights says government forces and members of Lebanon's Hezbollah group reached the Castello road Sunday, closing it and raising fears of a humanitarian crisis.

Government troops reached a point where they could fire on the road earlier this month, effectively cutting it off, though some people still made the dangerous journey.

Aleppo-based activist Bahaa al-Halaby told The Associated Press that rebel-held neighborhoods in the city are under "full siege."

The U.N. has warned that nearly 300,000 people rely on the Castello road for travel, food and medicine.