AMMAN (Reuters) - Plain-clothed police stationed near the presidential palace, a grey marble Soviet style compound towering over Damascus, fire automatic rifles into the night as rebels encroach towards the seat of Bashar al-Assad's power.
Gunmen guarding the luxury apartment of an intelligence officer nearby monitor incoming traffic from behind newly erected concrete walls and roadblocks that have become a familiar sight in residential neighborhoods, according to residents and diplomats in the capital.
Fifteen months into Syria's uprising, now coupled with an armed insurgency against Assad that is spreading from outlying regions, the rebels have infiltrated Damascus.
They are beginning to attack army and security strongpoints and fighting gun battles with loyalist troops, forcing Assad to devote more resources to protect Damascus and raising the once unlikely spectre that the capital could slip out of his grip.
The instability could spiral into full-fledged urban warfare, opening a new front for already stretched troops and increasing sectarian tension between Sunni inhabitants and Assad's minority Alawite sect, concentrated in hilltop enclaves overlooking the city of 3 million.
Alawites, an offshoot of Shi'ite Islam, already comprise the majority of the feared pro-Assad "shabbiha" militia as well as the Republican Guards and the Fourth Armoured division - core forces strategically based in mountains around Damascus under the command of Assad's brother Maher.
This has not stopped the Sunni-led protest movement from spreading into the heavily guarded capital, where army roadblocks and supply lines are coming under attack from lightly armed rebels.
When night falls, demonstrations that were once easily put down by the shabbiha break out under rebel protection, not far from central areas of the city. Aside from the protests, streets quickly empty of pedestrians and Assad's forces erect roadblocks separating the main districts, residents say.
A video broadcast by activists on YouTube, which could not be independently verified, showed crowds at an anti-Assad rally on Monday dancing and carrying huge white and green flags from the era before Assad's Baath Party took power in a coup in 1963.
"I think we're heading to the point where the regime will be only in control of the most central parts of Damascus and the airport road. It may able to continue mounting raids on other districts but it will not have real presence there," said a Western diplomat still in the city after many embassies have closed.
Gun battles have spread from the suburbs, which the army has struggled to control since the beginning of the year.
Residents say gunfire can now be heard daily in the northern residential neighborhoods of Barzeh and al-Qaboun, from which most inhabitants have fled, and in the Kafr Souseh district in the west, home to a fortress-like intelligence headquarters.
"It is becoming a cycle now. Troops fire at demonstrators in the morning and the rebels respond by attacking roadblocks and busses at night," said Lana, a businesswoman who lives in Kafr Souseh with her husband and three children.
"No one dares go out, and the troops manning the roadblocks become so nervous, especially at night. I mistakenly walked back from a friend's house at ten at night the other day and there was not a single soul in the streets. I made it. Others sometimes don't," she said.
She cited the case of Rabih Ghazza, a peaceful activist whose body was found stuffed in the trunk of his car near a security compound on Al-Khatib Street, adding that friends who went to pay condolences were beaten by the shabbiha.
The rebels, however, are fighting back.
On Friday rebels attacked shabbiha buses brought to quell protests in Qaboun, killing or wounding 20 militiamen and prompting security forces from the nearby Airforce Intelligence compound to fire anti-aircraft guns and heavy mortar rounds into the district, according to opposition campaigners.
It was the first time that the army had bombarded Damascus proper, they said, adding that troops backed by armoured personnel carriers deployed in Qaboun two days later and conducted house to house raids.
YouTube footage released by opposition activists also showed army trucks and soldiers in combat gear inside the Abbasid Football Stadium in Damascus, which has become a base for troops and militiamen confronting the opposition neighborhoods of Jobar, Zamalka and Irbin just to the east.
"The shabbiha used to come and shoot protesters in Irbin like flies. Now they do not dare to come without army protection," said one activist in Irbin, which regularly comes under army bombardment as rebels and troops clash in disused farmland on the edge of the capital.
In Old Damascus, popular with tourists before the uprising, bazaar merchants, long a core support group for the Alawite ruling elite, largely observed a week-long strike called after a massacre last month of more than 100 men, women and children in the town of Houla in Homs province, opposition sources said.
Julien Barnes-Dacey, senior policy fellow at the European Council on Foreign Relations, who was in the Syrian capital earlier this month, said the ferocity of the crackdown is alienating middle class Sunni Damascenes. Even some Christians who had supported Assad for fear of an Islamist ascendency, have started to turn against the Syrian leader.
Rising crime and worsening economic conditions - Barnes-Dacey saw long lines for cooking gas in the mixed quarter of Bab Sharki - are also contributing to the rise of the anti-Assad movement in Damascus.
"So far the sentiment within the capital is anti-regime rather than anti-Alawite. But this could change and we could see a more sectarian backlash as the crackdown intensifies," he said.
(Editing by Giles Elgood)