Streets leading into powerful Hezbollah's stronghold in the southern suburbs of the Lebanese capital have been cordoned off, as guards in civilian clothes search a long line of cars, AFP reports.
The Shiite militant group was already accused of running a "state-within-a-state," but two car bombings in the area in as many months have spurred Hezbollah to turn the suburbs into a fortress.
At entrances to "dahiyeh", or the suburbs, young loyalists of the group which has thrown its military weight behind Syria's embattled president order drivers to open up their car boots.
Others wear uniform, carry walkie-talkies and are members of the Hezbollah-run "Union of Municipalities of the Southern Suburbs".
They also stop and ask for the IDs of bikers entering the densely populated neighbourhood.
"It's time to be vigilant. People are more relaxed when they see us," a Hezbollah guard told AFP on condition of anonymity.
Backed by Tehran and a key ally of Syria's President Bashar al-Assad, the heavily armed Hezbollah suffered a severe blow on Thursday when a car bomb killed 27 people.
The attack, Lebanon's bloodiest since its 1975-1990 civil war, came just over a month on from another car bomb attack in the same area that wounded around 50 people.
Thursday's bombing was claimed by an unknown cell that said it was revenge for Hezbollah's engagement in Syria's war alongside Assad's troops.
Hezbollah chief Hassan Nasrallah accused radical Sunni Islamists of staging the attack.
Beyond the improvised checkpoints at main roads and bridges around the suburbs, drivers park their cars in cordoned-off streets and metal barriers block off alleyways.
In a country where critics accuse Hezbollah of using its arsenal to impose its will, such measures reinforce the fortress-like image of the southern suburbs, where the Lebanese army and police rarely venture.
The party has long worked in secret, especially when it comes to security. But today, its draconian measures appear to be making residents feel safer.
In the Rweiss area, near the target of the latest bomb attack, people conceal their fears when speaking to journalists.
"Naturally, everything has changed. This was a safe neighbourhood," said Moussa, a thirty-something who owns a lamp store damaged by the August 15 bombing.
But the man who "miraculously" survived the attack added: "We are not afraid. Even the Israelis couldn't scare us."
-- 'Syria's war has arrived here' --
Hezbollah fought a devastating summer war in 2006 against Israel, which used its air force to bombard the southern suburbs nightly for a month, flattening hundreds of apartment blocks.
Dahiyeh's defiance is vented on neighbourhood walls. "Never will we be humiliated," reads a sign posted on a building damaged in the latest bombing.
Hezbollah, meanwhile, has been getting to work repairing the damage, with members of the movement's Jihad al-Binaa (Struggle for Reconstruction) organisation fixing destroyed balconies.
After the 2006 war, it was this group that took charge of rebuilding southern Lebanon, outdoing the Lebanese government.
Hezbollah's Lebanese critics say the party itself is to blame for the bombing because it has sent troops across the border to fight in Syria.
But in the massively pro-Hezbollah neighbourhood, no one criticises the group, despite the anxieties the bombing has stirred.
"We hope there won't be any new attacks, thanks to God and the resistance (Hezbollah)," said Zeinab, a young mother of two girls.
Far from the gaze of Hezbollah's guards, other residents say they fear new car bombs.
"Everyone here is thinking, where will the next one hit? Ouzai? Hay al-Sellom?" said one man, Mohammed, referring to two neighbourhoods of the southern suburbs.
"Many Shiites have travelled to Iraq on pilgrimage, and they know what it's like there, the attacks, the checkpoints," he said.
People have started to fear that crowds and especially busy areas might be the targets of new bombings, like in Iraq.
"We think it's better to avoid popular markets, but what we're really worried about is the reopening of schools," Mohammed added.
Such fears are just as valid in other Hezbollah bastions.
In Baalbek in eastern Lebanon, armed men in civilian clothing inspect vehicles at night and have set up metallic barriers at the entrance to the city, an AFP journalist said.
Residents say that Syrians are the prime suspects in the attacks.
Because of Hezbollah's involvement in Syria's war, the conflict has spilled over into Lebanon.
"Syria's war has arrived here," said a young Hezbollah loyalist tasked with security in the Beirut suburbs. "And this is just the beginning."