BEIRUT (Reuters) - Fighting persisted in the Syrian city of Aleppo on Thursday more than an hour into a three-hour ceasefire announced by Russia, two rebel groups and a witness in the city said, as government forces tried to reverse last week's opposition gains.

Russia, which backs Syrian President Bashar al-Assad and his government, said on Wednesday daily ceasefires would last from 10 a.m. until 1 p.m. daily to facilitate the delivery of aid supplies.

Asked at 10.45 a.m. (0745 GMT) whether the ceasefire had taken effect, Mohammed Rasheed, spokesman for the rebel Jaish al-Nasr group, said: "No, on the contrary."

"Today since the morning there has been a (government) attempt to advance in the Ramousah area. There has been a big escalation by Russian warplanes," he added.

A witness in Aleppo near the frontline between the opposition-held eastern sector and the government-held west of the city also reported hearing continued fighting after 10.30 a.m.

A second rebel official said fighting was continuing at 11 a.m. local time.

Syrian state television reported on Thursday that the army had advanced on Wednesday night under cover of air strikes to positions near the areas that insurgents captured last week.

However, Rasheed of Jaish al-Nasr and Ahmed Hamaher of the Nour al Din al-Zinki group, which is also fighting in Aleppo, said government forces had taken some positions but then been quickly forced back.

(Reporting By Angus McDowall and John Davison; Editing by Gareth Jones)