Israeli police on Tuesday arrested 10 Jewish activists from an extremist group opposed to Arab-Jewish coexistence, including its leader, in the first major clampdown against a fringe organization that has become a symbol of rising anti-Arab sentiment.

Police said the crackdown followed a 10-month undercover investigation of "Lehava," known for its efforts to break up Arab-Jewish romances. The group has become increasingly visible in recent months amid rising tensions around a sensitive Jerusalem holy site and a wave of deadly Palestinian attacks.

Police spokesman Micky Rosenfeld said the arrests early Tuesday took place in Jerusalem and in the Hebron area of the West Bank, a region known for its hard-line Jewish settlements. He said the suspects were apprehended on suspicion of racist incitement and calls for "violent activity and terror."

On Monday, Israel also indicted three group members for allegedly torching a bilingual Hebrew-Arabic school in Jerusalem late last month where Arab and Jewish elementary and high school students study together.

"There is absolutely no place for these people in Israeli society," former Justice Minister Tzipi Livni told Israel Radio. "Our situation is simply too sensitive to allow it."

Lehava, which means "flame" and is also a Hebrew acronym for "The Prevention of Assimilation in the Holy Land," is made up of disaffected Israeli youths and ultranationalist religious Jews who oppose Arab-Jewish dating and coexistence. It is influenced by the teachings of the late Rabbi Meir Kahane, an ultranationalist whose Kach party was banned from parliament for its racist views in 1988. Kahane was killed by an Arab gunman in New York City in 1990.

Lehava activists have run vigilante patrols and telephone hotlines urging Jews not to date Arabs, issued flyers warning Arab men to stay away from Jewish areas, and waged campaigns to prevent Israeli employers from hiring Arab workers. In August, group activists staged a high-profile protest outside an Arab-Jewish wedding. At times of heightened tensions, its supporters have held demonstrations and chanted anti-Arab epithets, though it is unclear whether the group is behind these rallies.

Formed in 2009 by far-right activist and West Bank settler Bentzi Gopstein, the group primarily stayed on the fringes but rose in prominence this summer as tensions flared following the kidnapping and killing of three Israeli teens by Palestinian assailants, the revenge killing of a Palestinian teen, and a month of war between Israel and Hamas militants in the Gaza Strip. More recently, tensions have risen in Jerusalem, highlighted by violence around a sensitive holy site and a deadly Palestinian assault on a synagogue that killed five people.

In this tense atmosphere, the group's bumper stickers and posters have become a regular sight in Jerusalem, and it is common to see youths walking the streets wearing the group's yellow-on-black insignia, a flame burning inside a Star of David.

Lehava sets up a booth in Jerusalem's central downtown square twice a week, though left-wing activists monitoring the group report it has not held gatherings there since the three group members were arrested in connection with the torched school.

Other activists who have monitored the group at its public meetings say its leaders have discouraged violence and broken up a fight that broke out at one of them.

Activists communicate and mobilize using the mobile messaging app WhatsApp, said Avraham, a 19-year-old Lehava activist who declined to give his last name for fear of targeting by Israeli authorities. "Lots of people are beginning to understand that assimilation is bad for Judaism," the activist said.

The group's leaders say they oppose violence and are merely trying to prevent Jewish youths from assimilating. "Instead of giving me a prize for the important work I do to rescue the daughters of Israel, the state of Israel handcuffs me," Gopstein said at the courthouse Tuesday.

His wife, Anat, described a terrifying scene in their West Bank home during the early-morning police raid. "They searched our home, took pictures and books of Rabbi Kahane. They took cameras and computers and then they arrested him," she said.

Channel 2 TV showed pictures of a handcuffed Gopstein sitting in what appeared to be a living room, with police officers milling around. Wearing handcuffs on his arms and legs, he appeared in court, where his remand was extended.

The Israel Religious Action Center, a liberal Jewish watchdog group, said it had repeatedly petitioned Israeli authorities to act against the group in recent years.

"It shouldn't have waited for a school to burn," said Ruth Carmi, a lawyer for the group. "The writing was on the wall a lot earlier."