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Car bombings targeting Hezbollah strongholds south of Beirut have shaken the Shiite militant group, bringing fear to a community that was largely spared the violence plaguing the rest of Lebanon.

Nowadays, pistol-wielding Hezbollah operatives man checkpoints guarding the capital's southern suburbs, searching vehicles for explosives, frisking residents and occasionally deploying sniffer dogs.

Last week's massive car bombing that killed 27 people and wounded over 300 in the area was the second such bombing in five weeks and the deadliest one in nearly three decades.

It was also the first time the group's urban bastion, long considered a tightly-controlled state-within-a state, was targeted by bombers seeking to cause maximum civilian casualties as opposed to targeted assassinations. In a departure from its standard rhetoric, Hezbollah is not blaming its traditional foe Israel, but rather Sunni extremists for the attacks.

Many in Lebanon see the strikes as retaliation for Hezbollah's highly divisive and controversial armed support for President Bashar Assad in Syria's civil war. While there has been no credible claim of responsibility, Syrian rebels have threatened to hit back at the group for intervening on behalf of the Assad regime in a conflict that is being fought on increasingly sectarian lines, pitting Sunni Muslims against Shiites.

The violence has sent the group's supporters into unchartered territory. For now, they are closing ranks and voicing unflinching support for the leadership. But recurrent attacks could eventually create new dynamics that loosen Hezbollah's hold over its Shiite constituency.

"Hezbollah is really testing the tolerance level of its support base," said Bilal Saab, director of the Institute for Near East and Gulf Military Analysis, North America.

Over the past few months, Beirut's predominantly Shiite southern suburb known as Dahyeh (Arabic for suburb) has been rocketed several times, while several Hezbollah cadres were targeted by roadside bombings near the border with Syria. On July 9, a car bomb wounded more than 50 people in an area not far from Thursday's massive bombing.

While Lebanon has seen numerous bombings and assassinations since the end of its 1975-90 civil war, until now almost all of them had targeted Christian and Sunni anti-Syrian leaders.

Thursday's explosion was the single deadliest blast in the stronghold since 1985, when an explosives truck targeted a top Shiite cleric and spiritual mentor to Hezbollah, killing 80 people.

The bombings raise the specter of Iraqi-style sectarian conflict in Lebanon, a daunting prospect for Hezbollah, which is facing some of its toughest challenges yet since its founding in 1982 to fight Israeli occupation.

At sunset on Monday, an AP reporter observed three Hezbollah checkpoints at the entrances to Dahyeh manned by men carrying pistols and walkie-talkies. Hezbollah operatives stopped most cars and searched their trunks, leading to lines that stretched up to 100 meters (yards) and slowing down business in the normally vibrant area.

On Tuesday, the Lebanese army replaced Hezbollah at the entrance checkpoints, although Hezbollah members continued to handle security inside.

Residents in the area said the bombings and security measures would not alter their support for Hezbollah leadership. At a candlelight vigil held Monday evening near the location of Thursday's bombing, the mood among some 1,000 participants was defiant.

"To the killer we say, Dahyeh is steadfast," read one poster.

"The security measures are excellent and they make us feel safe," said Ghaleb Ismail, 59, who suffered bruises on his leg when Thursday's blast knocked him off a motorcycle. "We love the party and we worry about it," he added.

Fadi Nasrallah, a 36-year-old chef, said Hezbollah's measures "reassure us and all Lebanese."

"This is in the people's interest because the whole world is conspiring against us," said Nasrallah, as he carried his nine-month-old son, Ali al-Rida, wrapped in a Lebanese red, white and green flag.

In a speech to supporters on Friday, a day after the bombing, Hezbollah leader Sheik Hassan Nasrallah said he was not worried about his Shiite constituency losing its resolve, adding that they have been through much worse.

"We recognize your patience and courage, your understanding and loyalty. This is not emotional talk. We have experienced this throughout the past decades," Nasrallah said, citing the monthlong war against Israel in 2006 when much of Dahyeh was leveled by Israeli airstrikes.

Indeed, it is difficult to imagine Hezbollah supporters cutting ties with the group the next time a bomb goes off in their neighborhood. The Iranian-backed political movement, whose name means "Party of God," has spent decades cultivating Shiite support and has deep political and social roots in Lebanon.

The group runs a sophisticated network of schools, clinics and social services in the Shiite community and also assists in relief efforts.

On Tuesday, its reconstruction arm, Jihad al-Bina, busily surveyed damage from the bombing and began to repair buildings from scaffolding.

Hezbollah's popularity, however, which ran high in the Arab world during the 2006 war, has sharply declined in recent years, largely because of its position regarding Syria's civil war. Fighters from the group helped propel Assad's forces to victory in the strategic town of Qusair near the border with Lebanon in June. Now, its staunch support for Assad overshadows its former image among Arabs as a heroic resistance movement that stood up to Israel.

In Lebanon, a deeply polarized nation, the group is increasingly accused of putting the interests of longtime patrons Iran and Syria over those of its home country.

Ali Hamadeh, a columnist for Lebanon's leading An-Nahar newspaper, on Tuesday urged Lebanon to hold the group accountable for exposing the country to terrorist threats because of its open involvement in Syria.

Analysts say recurrent attacks to Hezbollah strongholds could eventually challenge its authority among Shiites as increased fear and anxiety sets in, although Lebanon's sectarian makeup and poor state services leave Shiites with few other leadership options.

"Given the absence of a credible and reliable alternative, it will be very difficult for Shiites to break with Hezbollah," said Saab, the analyst.

"A rallying around the flag effect should not be dismissed."

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Follow Bassem Mroue on http://twitter/bmroue and Zeina Karam on http://twitter/zkaram .