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BEIRUT, Sept 27 (Reuters) - Pro-Syrian government forces were mobilising on Tuesday for a ground attack in Aleppo after attacking on four fronts in their largest assault since launching a campaign to retake the whole city last week, a senior rebel official said.

Separately, an Iraqi militia commander fighting in support of the government told Reuters a large army force, spearheaded by an elite unit known as the Nimr, or Tiger Forces, had started to move in armoured vehicles and tanks for an attack on rebel-held districts of eastern Aleppo.

Pro-government forces attacked at the same time around the Handarat camp north of Aleppo, at the nearby Kindi Hospital area, in the Rashidin district in the centre of the city and at the 1070 Apartments in the southwest.

Government forces briefly captured Handarat from rebels on Saturday, only to lose it in a counter-attack hours later.

The senior rebel official said the simultaneous attacks had been repelled, but pro-government forces were also mobilising in two other areas near the rebel-held Sheikh Saeed district on the city's southern outskirts.

"They are working to expand on any opening they create," said the official from an Aleppo-based rebel faction, citing reports from his fighters. "Today, the other noticeable thing is the heavy use of helicopters and barrel bombs."

The Syrian military, helped by Iranian-backed Shi'ite militias and the Russian air force, launched a major campaign to take rebel-held eastern Aleppo last Thursday.

(Reporting by Tom Perry and Laila Bassam; Editing by Robin Pomeroy) ((thomas.perry@thomsonreuters.com; Reuters Messaging: thomas.perry.reuters.com@reuters.net))