Correction: An earlier version of this article incorrectly said that the population of the West Bank city of Hebron, according to its mayor, is 750,000. In fact, Mayor Daoud Zatari was referring to the larger Hebron governorate, or district. This version has been corrected.

Israeli security forces are carrying out night raids and mass arrests in one of the largest security sweeps seen here in years as they intensify their search for three missing teenagers that Israel says were kidnapped by members of the Islamist militant organization Hamas.

Military drones circled and tethered-observation balloons hovered over Hebron on the third day of a lockdown by Israeli forces, nearly four days after the teens disappeared on the outskirts of town.

As the security cordon tightened, Palestinian Authority President Mahmoud Abbas on Monday condemned, for the first time, the kidnapping of the missing students, ages 16 to 19, who vanished Thursday night while hitchhiking home from their religious schools in the Israeli-occupied West Bank.

Abbas also denounced the ongoing Israeli military response to the disappearances, which resulted in the killing of one Palestinian in a clash with Israeli soldiers at a refugee camp outside Ramallah. More than 150 Palestinians have been arrested in connection with the case.

Daoud Zatari, mayor of Hebron, said in an interview that he visited two of the homes raided early Monday by Israeli forces. The troops used explosives to enter the houses and brought dogs, and they scattered food and belongings on the floors, he said.

“I’ve never seen anything like this before here,” Zatari said. “Not even in the worst years” of the Israeli-Palestinian conflict.

The mayor accused Israel of enforcing a collective punishment on the residents of Hebron, who have seen the main entrance into the city closed by Israeli authorities and their roads rumbling with troop convoys.

“We are in the midst of a complex operation,” Israeli Prime Minister Benjamin Netanyahu said Monday. “We need to be prepared for the possibility that it may take time.”

Israeli security forces have declined to offer any evidence that Hamas is behind the abductions, partly because the investigation is ongoing, they say. But their sweep has focused on members of Hamas, a movement that controls the Gaza Strip and is considered a terrorist organization by Israel and the United States.

The West Bank is governed by the Palestinian Authority, dominated by the Fatah political party of Abbas, which recently won the support of longtime rival Hamas to form a transitional Palestinian unity government. That deal has been roundly criticized by Israel, which in recent days has said it would hold Abbas accountable for the kidnappings it says were carried out by Hamas.

Netanyahu reiterated that message in a telephone call with Abbas on Monday, their first in nearly a year.

“I expect you to assist in returning the abducted youths and in apprehending the kidnappers,” Netanyahu told Abbas during the conversation, according to the prime minister’s office. “The Hamas kidnappers came from territory under Palestinian Authority control and returned to territory under Palestinian Authority control.”

Naftali Frankel, from left, who also holds U.S. citizenship, Gil-ad Sha'er and Eyal Yifrach are seen in this combination picture of undated family handout photos. (Handout/Reuters)

Among the 150 arrested in the past two days were senior Hamas leaders, including the speaker of the Palestinian Legislative Council, Aziz Duweik.

Anas Duweik, the son of the arrested parliamentarian, said his 67-year-old father was taken in the pre-dawn hours Monday from his home in Hebron.

“My father has a clear political role. He meets with the media every day. He is not involved in anything underground,” he said in an interview.

He said his father had nothing to do with the abductions.

“The Israelis want to show they are doing something,” so they have arrested Hamas leaders, Duweik said.

Lt. Col. Peter Lerner, an Israeli military spokesman, said the arrests of Hamas leaders are focused on “enhancing intelligence and influencing those that participated, are involved or have knowledge of the whereabouts of the missing teens.”

Lerner said the raids in Hebron are conducted in a way that “ensures the safety of Israeli soldiers” and “done in a professional manner.”

In Hebron on Monday, the streets were emptied and shops closed as citizens answered a call to show their solidarity with 120 Palestinian detainees in Israeli prisons who have reached Day 54 of a hunger strike. The prisoners are protesting being jailed without charges or trials, in a system Israelis call “administrative detention.”

“I am asking them to remain calm,” the Hebron mayor said.

Netanyahu said Monday that Israel would continue to retaliate against attacks from Gaza, where Hamas is in charge of security.

Last week in the northern Gaza Strip, Israelis carried out the targeted killing of 33-year-old Mahmed Awwar, who they said was responsible for rocket attacks against Israel. Awwar’s 7-year-old nephew, who was riding with him at the time, died four days later of his injuries.

Since then, at least five rockets have been fired from the Gaza Strip at Israel, said Lt. Libby Weiss, an Israeli military spokeswoman. On Saturday and Sunday, Israel responded with airstrikes, hitting what it called terror sites and weapons facilities. Two women in Gaza were injured in the strikes, according to Gaza media reports.

Egalsh reported from Jerusalem.