| ALEPPO, Syria
ALEPPO, Syria Four men from the rebel Free Syrian Army check their assault rifles and sling them over their shoulders.
Their commander, Abu Thabet, calls them over to give final instructions before they head through the deadly, sniper-ridden neighborhood of Salaheddine in Aleppo.
"Keep your heads down, stick close to the sides of the buildings and walk fast," he tells them.
Aleppo, Syria's biggest city and the engine room of its economy, is seen as a vital prize by both sides in the 17-month-old uprising against President Bashar al-Assad.
A Reuters crew joined the group from the Seyoof al-Shahbaa brigade on its way to reinforce 20 of their men.
Rebels took control of Salaheddine early this month but last week troops backed by tanks, warplanes and helicopter gunships launched a fierce offensive to drive them out.
Army snipers are now posted in the area, a southern gateway to Aleppo, after tanks and jets battered rebels for days.
Rebels short of ammunition are up against Assad's superior firepower, even if tanks are hard to maneuver through narrow residential streets in this city of 2.5 million.
Abu Thabet's men walk into the edge of Salaheddine in single file, hugging the buildings and tightly clutching their rifles.
In fatigues and a sleeveless T-shirt, their leader's left arm lies in a sling after a piece of shrapnel broke his shoulder a few days ago. In his good hand he holds a pistol.
On either side of the ghostly empty streets, flies buzz over huge piles of rotting garbage.
High in a building, a rebel sits on a windowsill, barefoot and holding a rifle ready to return fire on any army snipers.
Clambering up the fallen concrete using a makeshift wooden ladder, the group enters a bombed-out building. Abu Thabet's men have broken holes in the walls to create safe passages for them to move around in Salaheddine, out of the snipers' sights.
"Now we are on a street parallel to Al-Albesa Street," Abu Thabet explained. "On our right are snipers and on our left snipers. So we will go through these buildings to get to the Salaheddine roundabout."
This building takes them into a maze of holes through deserted homes and apartment hallways back to back until they reach the roundabout that for now marks the frontline.
The holes in the walls are tight and their edges jagged with broken brick. Rebels squeeze through, legs first, then arms, scratching their skin and turning their hair white with dust.
There is evidence of abandoned lives all around.
A prayer mat lies on the floor of an empty bedroom. Another room has a cabinet filled with china tea cups and crystal glasses. A bird cage stands empty. In a kitchen, a jar of pickles sits half-eaten and rotting on the counter, flies circle around a pile of dishes in the sink.
In one apartment, rebels use the master bedroom as a weapons depot, placing ammunition and rocket-propelled grenades (RPGs) on top of the red blanket covering a bed.
The hallways are dim and the zig-zag route, up stairs, through bedrooms, from apartment to apartment, makes it hard to keep track of how many buildings have been traversed.
The last hole is through a large wooden closet, its back smashed through and behind it a gap two meters (six feet) wide, opening into an apartment filled with water bottles and bread.
About five rebels are crammed in a hallway waiting for orders. In a small living room a candle lights up a sofa set and family pictures sitting on a small television.
"We are now at the Salaheddine roundabout. The new frontline of the battle of Aleppo," announced Abu Thabet, walking out into the bright street. "The army is just behind this building."
At the edge of the small street facing the roundabout, a group of five rebels take cover behind a broken wall.
"The army is advancing into the Salaheddine roundabout and bringing more reinforcements," said Abu Yazen, 29, an army defector who was in charge of the fighters at the roundabout.
"Their strategy now is to try to break the walls of the buildings around us so that they can advance and take our positions," he said.
Sniper fire starts up, the bullets snapping through the air overhead.
Suddenly, the slow rumble of a tank could be heard from one street over. "Tank, tank, tank," yelled one man.
Quickly, a rebel shifted an RPG over his shoulder and skipped down to squat on the rubble-filled ground.
"Allahu akbar, Allahu akbar (God is greatest)," shouted one man, raising his arms over his head encouraging the men to join him. All 20 men screamed: "Allahu akbar, Allahu akbar."
Seconds later, the RPG goes off with a swoosh and boom.
"I got it, I got it," cried the man who fired it, as his comrade prepared a new grenade, twisting its cone-shaped head onto the launcher.
Then the mundane bleep of a text message, a government announcement claiming its forces control Salaheddine and have cleansed it of rebels. The men laugh.
But minutes later, a tank shell flies overhead and explodes on a building nearby, deafening ears.
Then another tank shell booms, and the rebels fire another RPG, only to be met with a rain of mortar bombs filling the sky with smoke and shrapnel. "They're going to send more mortars. Hide in the doorway," Abu Yazen screams.
Panicked rebels told journalists to leave for their own safety.
"They're taking revenge, they're going to mortar this place to bits," shouts one rebel waving his automatic rifle.
On the way back, more mortar rounds land and a nearby building is shelled, sending an electricity pole crashing down, cables swinging wildly to the ground.
Five tank shells explode. The air is thick with hissing, burning, black smoke. Warplanes rumble overhead, firing downwards.
(Editing by Oliver Holmes and Alistair Lyon)