ALEPPO, Syria (AP) — Syrian warplanes, artillery and mortar rounds pounded areas in eastern Aleppo on Saturday drawing rebel rockets, as government troops gain new ground in the shrinking opposition-held enclave.

After four years of holding nearly half of the divided city, rebel fighters have been increasingly squeezed into the center of the eastern enclave. Government and allied troops, including Lebanese, Iraqi and Iranian fighters, have concentrated their fight on the northeastern part of the enclave, swiftly taking new districts since their offensive began last week. Another front on the southern outskirts of the city has been slower, as rebel fighters push back government advances there.

The advances have caused massive displacement. The U.N. estimated that more than 31,000 have already fled their homes, either to government or Kurdish areas, or deeper into the besieged enclave. The fighting has also intensified the rebel shelling of government-held areas in Aleppo.

The state broadcaster al-Ikhbariya said "precise operations" by government and allied troops aim to rout out "terrorists," which is how the government refers to all armed opposition groups.

The sound of war prevailed in the city early Saturday. Warplanes made several runs overhead, drawing what appeared to be rebel machine gun fire toward the aircraft.

The Syrian Civil Defense in eastern Aleppo said six people were killed in bombings of the central al-Shaar neighborhood. Opposition news agency Thiqa also put the death toll at six. The Britain-based Syrian Observatory for Human Rights put the death toll at three, adding it was likely to rise. In government-held Aleppo, rebel shelling killed five people, according to the state news agency SANA.

To the south of the city, government cannons could be heard firing toward rebel-held areas.

Residents in eastern Aleppo also reported intense shelling in al-Sukkari neighborhood on the southern edge of the enclave, where many of the newly displaced have sought refuge.

"The noose is tightening quickly," said Mohammed Abu Jaafar, a medical official in besieged eastern Aleppo. "Our resources are also running low and beginning to disappear."

The bombings Saturday came hours after government troops made new advances on eastern parts of the enclave, including in Tariq al-Bab and al-Khaterji districts. State media reported that government and allied troops have moved in on new neighborhoods, pushing one kilometer (0.6 mile) deeper into the enclave from the far east.

The new advances tighten the government's grip on the enclave and reduce the territory the rebels hold by more than half, according to the Observatory.

The new advances also secure the airport road east of Aleppo, leading to the city's international airport and a military airbase. The pan-Arab Mayadeen TV station said intense bombing in eastern Aleppo was designed to ensure rebels have been cleared from the airport road.

Moscow, a main backer of the Syrian government, says its warplanes haven't bombed Aleppo since Oct. 18. But the Russian military has helped fend off rebel attempts to break the siege of the city.