DAMASCUS, Dec. 6 (Xinhua) -- Syrian government forces on Tuesday entered the old city of Aleppo, controlling some three quarters of the eastern territory of the besieged Syrian city that had been under the rebel control for nearly five years.

The rebels withdrew towards the southeastern neighborhoods, pan-Arab al-Mayadeen TV reported.

The Syrian government troops retook seven districts from the rebels. The military advance was made after they stormed the strategic al-Sha'ar neighborhood, the main stronghold for the al-Qaida-linked Nusra Front in the rebel-held part east of Aleppo.

An eye witness in Aleppo told Xinhua over the phone that celebratory gunshots reverberated across the government-controlled parts in the west of Aleppo on Tuesday evening.

The military gain came after a two-week-long major offensive the Syrian army launched after imposing a siege. They said they will press on with the operation until the recapture of all the rebel-held areas in eastern Aleppo.

Over 30,000 civilians fled eastern Aleppo to the government-controlled west, and the Syrian government has pledged help to relocate people there. Humanitarian organizations have raised alarm about the situation of 250,000 people living in eastern Aleppo.

Russian Foreign Minister Sergei Lavrov said talks with the United States on a rebel withdrawal would begin in Geneva as early as Tuesday evening or Wednesday morning.

The Syrian government said it now rejects any cease-fire for Aleppo, which it fears would be used by the rebels as a chance to "regroup."

Russia and China on Monday vetoed a United Nations Security Council draft resolution on a seven-day humanitarian truce in the northern Syrian city.

Liu Jieyi, China's permanent representative to the UN, said China remained committed to an early political solution to the Syrian crisis, which works on "the four tracks of resumption of cease-fire, political peace talks, cooperation in counter-terrorism and humanitarian relief."

Lebanon's Prime Minister-designate Saad Hariri on Monday expressed support for China's stand while meeting with visiting Special Envoy of the Chinese Government on Syrian issue Xie Xiaoyan in Beirut.

He said he appreciated China's stand, and hoped that China will play a larger role on the Syrian issue.