* Power out for first time in central districts
* Clashes half a mile from Old City
* Shells land near Russian embassy
By Oliver Holmes
BEIRUT, Jan 21 (Reuters) - Residents of central Damascus said they spent Sunday night without power as rebels fought Syrian troops half a mile from the Old City in the heart of the capital.
Long a stronghold of President Bashar al-Assad, central Damascus is increasingly feeling the impact of a slow advance by rebel fighters who control a crescent of suburbs to the east and south of the city. The price of basic commodities has soared and fuel shortages are affecting services.
"The power went out all over the city including areas that have usually been ok," said a resident, who asked not to be named for security reasons.
She said it was the first time during the 22-month-old uprising that has turned into a civil war that the most central parts of the capital were affected.
State news agency SANA quoted the Minister of Electricity Imad Khamis as saying terrorists - a term the government uses for rebels - had attacked a main electricity line, causing the outage. Power returned to some areas on Monday.
The resident said power went out including in the upscale district where Assad and his cousin, business tycoon Rami Makhlouf, have homes.
"(Makhlouf) lives in an apartment building and the first floor of the building is strictly security. Last night, the floor in that building was the only one lit in the entire neighbourhood," the resident said.
She said militiamen with tattoos of Hafez al-Assad, Bashar's father and the former president, stood guard outside.
More than 60,000 people have been killed, according to United Nations estimates, in the longest and bloodiest of the Arab Spring revolts.
For much of the revolt, Damascus was spared the worst violence. Now rebels are fighting 800 metres (half a mile) from the Old City, once a tourist haven and a UNESCO World Heritage Site where several religious groups live side by side.
When rebels entered the ancient city of northern Aleppo, the area was bombed by government forces. Clashes led to a fire which destroyed parts of the ancient souk and the 8th-century Great Mosque was damaged.
"Inside Damascus' Old City, you can't escape the muffled sounds of shelling and fighter jets and even machineguns fired off nearby," said the resident, who visited the area on Sunday.
The government sent reinforcements to the rebel-held southwestern district of Daraya on Monday, the Britain-based Syrian Observatory for Human Rights said. Infantry and personnel carriers arrived on the outskirts of the district which has seen months of artillery and air strikes, it said.
On Saturday, two shells landed near the Russian embassy, hitting a wedding hall and killing three women, one of the hall's guards said. It was not clear who fired the shells. The area is government controlled.
Russia has blocked three United Nations Security Council resolutions condemning Assad and has supplied his armed forces with helicopters and jets.
The Russian embassy, which is along Damascus' central al-Thawra road, is heavily fortified with cement road blocks and the area has been blocked off. (Editing by Janet Lawrence)