ANTAKYA, Turkey—Fighting returned to the besieged Syrian city of Aleppo on Sunday following the end of a three-day humanitarian cease-fire that expired with no planned aid deliveries or medical evacuations.

Russia implemented the cease-fire along with Syrian armed forces loyal to President Bashar al-Assad to allow the entry of humanitarian aid into the city.

Moscow billed the move as an opening for residents and rebels to leave opposition-controlled neighborhoods. But no aid arrived and rebel factions vowed to remain and continue fighting.

Jens Laerke, spokesman for the United Nations Office for the Coordination of Humanitarian Affairs, said assistance couldn't be delivered because of security conditions. Russia's Defense Ministry didn't respond to requests for comment.

In photos and videos posted online, residents of the eastern half of Aleppo were seen using the pause from weeks of intense bombardment and airstrikes to protest the Assad regime and declare they wouldn't leave their homes.

A government sniper targeted a small number of civilians who attempted to cross over to the regime-controlled part of the city on Thursday, residents and medical officials said. The Syrian regime has denied targeting civilians.​

Soon after the cease-fire ended late Saturday, the regime began a bombardment and tried to advance along numerous front lines in the city and its countryside, backed by foreign Shiite militias. By early Sunday, many of the clashes had subsided after rebels inflicted losses among the regime forces, several rebels said.

Last week, U.N. envoy for Syria Staffan de Mistura said part of the plan for the temporary cease-fire was to allow for the voluntary departure of fighters with the opposition Syrian Conquest Front, formerly the al Qaeda-linked Nusra Front.

Despite the group's recent break with al Qaeda, it is still designated as a terrorist group by the U.S., which has proposed working jointly with Russia to target both the Syrian Conquest Front and Islamic State.

U.S.-backed and Islamist rebels have said the regime and Russia have used the presence of the formerly al Qaeda-linked fighters as a pretext to launch attacks on mainstream opposition fighters. The Assad regime has maintained that all opposition forces are terrorists.

A previous cease-fire brokered by U.S. and Russia collapsed on Sept. 19 and since then the Syrian regime backed by Russian airstrikes has launched an offensive to retake the entire city of Aleppo.

The Assad regime has been dropping fliers and sending text messages to residents in eastern Aleppo urging them to abandon the rebels and return to the fold of the Syrian government.

Meanwhile, rebel factions said they were preparing an offensive to break the siege themselves and allow food and fuel to reach nearly 300,000 people blockaded inside the eastern neighborhoods.

Rebel groups were able to briefly open a road into Aleppo in August but quickly lost ground to regime forces and their allies, who reimposed the blockade. Since then food, fuel and medicine supplies have dwindled and residents are living off meager rations.

Thomas Grove

Write to Raja Abdulrahim at raja.abdulrahim@wsj.com

(END) Dow Jones Newswires

October 23, 2016 23:25 ET (03:25 GMT)

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