Updated

The masked men came in the night, ripped off the front door and set the bookstore on fire. They were out to punish the owner, an elderly priest, after false rumors that he had written an anti-Islamic tract.

Thousands of books that lined the walls became the latest victim of Lebanon's sectarian tensions, which have been swelling as civil war rages in neighboring Syria.

But the blaze in the northern city of Tripoli also moved many residents, Muslims and Christians alike, to offer to help repair the 40-year-old shop, showing how some Lebanese are rising up in protest. The outpouring echoes a similar response last month after a teenager was killed in a car bombing that targeted a prominent politician in the Lebanese capital. His death ignited protests and an online campaign.

On Sunday, a day after the fire, a dozen activists gathered in an arched alleyway outside the Saeh bookstore. A music box blared the melancholy song "I Love You, Lebanon" by the country's beloved singer Fairouz. A Lebanese army tank was parked at the end of the street, and soldiers in blue-and-khaki camouflage uniforms milled about. A young man with shaggy hair scrubbed soot off the alley's stone floor with a broom, assisted by a middle-aged Muslim woman in a headscarf.

"Most of the people who came don't know the bookstore," said Mutaz Salloum, a 26-year-old volunteer. "There's always fighting, bombs and attacks on people's property. People are really sick of it. We can't be quiet anymore."

The crammed and sagging building that housed the Saeh was still pockmarked by bullets from Lebanon's 15-year civil war that ended in 1990. A woman carried off charred books from the shop, its shelves still stuffed with works ranging from Abdul Razzaq al-Husseini's "Political and Contemporary History of Iraq" to a French translation of Virginia Woolf's "Orlando."

The shop's most valuable items, centuries-old religious manuscripts, were mostly unharmed. They included 40 copies of the Muslim holy book, the Quran, written in delicate calligraphy, said book collector Maurice Kodeih, who was in touch with the media-shy Greek Orthodox priest who owns the shop, Ibrahim Sarrouj.

Najat Bitar, a relative of the priest, said it appeared that no more than a fifth of the shop's' estimated 80,000 books were burned, thanks to high humidity in the creaky building. Still, it wasn't clear when the bookshop would reopen or the cost of the damages.

The attack was not unexpected, Bitar said. Just two days earlier, gunmen entered the shop and fired at an employee. Bitar said they called the police, who took in Sarrouj for questioning, asking him if he had written an anti-Islamic tract.

Sarrouj, who has worked for years in interfaith Muslim-Christian relations, told police it was the first he'd heard of the tract, according to Bitar. The tract in question was published years ago and can be found online.

The following day, security officials told the priest that Muslims from a nearby mosque intended to demonstrate against him. The officials assured the priest that they would prevent protesters from entering the shop. They sent soldiers, and the protest fizzled out.

An Interior Ministry official said authorities were investigating the arson attack but that he could not provide more information.

Bitar and other relatives said the owners of the building had harassed Sarrouj for years to move, hoping to tear it down, but that they did not know if that had anything to do with attack early Saturday. The owners could not be reached for comment.

"I do not want to speculate too much," said the priest in a terse television interview with The Associated Press.

But what was frightening, said residents, was that regardless of the arsonists' real motives, the rumor was spread as a way of justifying the fire.

Violence has been increasing in Lebanon between rival Muslim sects, exacerbated by the three-year uprising next door against Syrian President Bashar Assad. Sunnis have mainly lined up behind Syria's rebels, while Shiites back Assad.

Lebanese Christians have largely remained on the sidelines, but the growing tensions appear to have given new blood to old grievances of Muslim extremists who accuse Christians of defaming their faith. The issue is particularly sensitive in Tripoli, a majority Muslim city with a sizeable Christian minority north of the Lebanese capital, Beirut.

Hard-line Sunni clerics hold sway in the city's mosques, and their followers form a key bastion of Islamic militancy in Lebanon.

Rattled residents, Christian and Muslim, said they think the bookstore was burned to revive tensions between the two faiths, with some noting that many Christians have moved in recent years to Christian villages surrounding the city.

"Nobody is happy with the situation like this," said Amal, 46-year-old Christian woman. She declined to give her family name, fearing the arsonists.

Lebanese politicians and religious scholars rushed to denounce the arson attack, visiting Sarrouj and his bookshop to show solidarity. The culture minister, Gaby Leon, donated 1,000 books.

Amid the despair, residents pointed to the rush of volunteers from Lebanon's many sects.

"They are the one hope for his country," Bitar said, pointing to young women wearing Muslim headscarves packing away books.

Sarrouj said he was deeply touched by the response.

"I thank the Lord for this. It bought people together," he said. "Muslim, Christians, maybe atheists, all of them they came together to rebuild the bookstore and to make it better than it was. This is what is more important for me."