(Adds detail, quotes, rebel shelling, government bombardment)
BEIRUT, Dec 5 (Reuters) - Syrian government forces and their allies advanced into another rebel-held part of eastern Aleppo, a rebel official and the Syrian Observatory for Human Rights said on Monday, as the army drew closer to opposition-held parts of the Old City.
A Reuters journalist in government-held western Aleppo said rebels had shelled government-held districts on Monday, especially near the frontlines, and plumes of smoke could be seen rising from an area of the Old City.
The Observatory said government forces had bombarded rebel-held areas of eastern Aleppo intensely since midnight.
Having captured swathes of eastern Aleppo from rebels in the last two weeks, the army and its allies are seeking to drive a wedge between the al-Shaar neighbourhood and the remaining part of rebel-held eastern Aleppo to the southwest.
The rebels defending al-Shaar may be forced to abandon it or risk being cut off from the other areas, rebel sources say.
The Syrian army could not immediately be reached for comment.
"The regime advanced (into al-Shaar) and there were clashes all night. The clashes are still going on," said Zakaria Malahifji, a Turkey-based official with the Aleppo rebel group Fastaqim.
A fighter with the Nour al-Din al-Zinki group in Aleppo said government forces had made advances on several fronts, putting al-Shaar under pressure, but it had not yet been besieged. The fighter spoke in a voice message sent to Reuters from the city.
A rebel official in a third rebel group, the Jabha Shamiya, said al-Shaar had effectively fallen since government forces seized nearby areas that control access to it.
"Karm al-Jabal and al-Shaar are considered fallen," the official with the Jabha Shamiya group told Reuters, speaking from Turkey.
The Syrian Observatory for Human Rights, a Britain-based war monitor, reported heavy clashes on Monday in al-Shaar. The Syrian army and its allies captured parts of the district, it said.
Aleppo has for years been divided between the government-held west and rebel-held east, where the army and its allies have made a sweeping advance since last week. (Reporting by Tom Perry, Ellen Francis in Beirut, and Suleiman al-Khalidi in Amman; Editing by Janet Lawrence)
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