Israel launched the most intense airstrikes on the occupied West Bank in nearly two decades on Monday, saying it was trying to root out armed militants in the city of Jenin after a year of escalating violence there. At least eight Palestinians were killed.

The Israeli military said the operation began shortly after 1 a.m. with drone attacks from the air on what it called “terrorist infrastructure” in the Jenin area, followed by hundreds of ground forces moving in. Military officials said the operation focused on militant targets in the densely populated Jenin refugee camp, an area of less than a quarter of a square mile abutting the city, with about 17,000 residents.

Israel estimates that there are hundreds of armed Palestinian militants in the Jenin area, which has recently been the focus of attacks against Israelis and deadly Israeli Army arrest raids.

Long a symbol of Palestinian militancy and a haven for armed groups opposing Israel’s occupation of the West Bank, Jenin is a stronghold of the Iran-backed Islamic Jihad group and of Hamas, the Islamic militant group that controls the Palestinian enclave of Gaza. Israeli military officials say more than 50 shooting attacks have been carried out from the Jenin area against Israeli targets in the past six months.

Army arrest raids have led to increasingly fierce exchanges of fire between the troops and the militants, prompting Monday’s incursion.

“The camp is a war zone in the full meaning of the word,” Muhammad Sbaghi, a member of the local committee that helps administer the Jenin camp, said after the operation began on Monday. He added that residents had feared a large-scale incursion by the Israeli military but had not expected something so violent and destructive.

“The occupation army is vindictively targeting us,” he said. “People are terrified,” he added, saying that residents were holed up in their homes throughout the Jenin refugee camp.

A spokesman for the Israeli military, Lt. Col. Richard Hecht, said the goal of the Israeli operation was “to break the safe-haven mind-set” of the refugee camp. At least 19 people suspected of attacks on Israelis had found shelter there in recent months, according to the military.

Colonel Hecht said the airstrikes were intended to “minimize friction” on the ground and the risk to Israeli troops, adding that the assault would go on for “as long as needed.” Ground forces inside the camp were seizing weapons, he said.

Israeli media reports estimated that about 1,000 ground troops were in Jenin as part of the operation.

The Palestinian health ministry confirmed that at least eight Palestinians had been killed in Jenin and about 50 were wounded, 10 of them gravely. Israel said it had killed at least seven people it identified as armed suspects.

The military described the city of Jenin and the camp on Monday as “an active combat area” and said exchanges of fire were continuing there.

The military said missiles fired from Israeli drones had struck a joint operations center used by militants of the Jenin Brigade in the refugee camp. Israeli forces also targeted a facility for weapons production and explosive device storage, and located and confiscated an improvised rocket launcher, the military said.

A map issued by the military indicated that the operations center in the camp was near several compounds run by the United Nations Relief and Works Agency, which provides services for Palestinian refugees.

Residents of the northern West Bank have recently been witnessing an explosive mix of violence. There are attacks on Israelis by armed local Palestinian militias; almost daily arrest raids by the Israeli military; and reprisals by extremist Jewish settlers, who have rampaged through Palestinian villages setting fire to property.

This year has been one of the deadliest so far for Palestinians in the West Bank in more than a decade, with more than 140 deaths over the past six months. Most were killed in armed clashes during military raids, though some were bystanders. It has also been one of the deadliest years for Israelis in some time, with nearly 30 killed in Arab attacks.

Increasingly, as in other areas of the northern West Bank, armed militias like the one known as the Jenin Brigade have sprung up in Jenin. Made up of members of established groups as well as unaffiliated gunmen, they act independently of the main organizational structures.

The last time Israel carried out such extensive airstrikes in the West Bank was during the second Palestinian intifada, or uprising, of the early 2000s.

Israeli officials said early Monday that they had been in contact with representatives of the Palestinian Authority, the provisional body created under the Oslo peace process in the mid-1990s to exercise limited self-rule in parts of the West Bank. They were also in contact with authorities in neighboring Jordan.

The spokesman for the Palestinian presidency, Nabil Abu Rudeineh, denounced the Israeli assault on Jenin as “ a new war crime against our defenseless people,” according to Wafa, the official Palestinian news agency.

“Our Palestinian people will not kneel, will not surrender, will not raise the white flag, and will remain steadfast on their land in the face of this brutal aggression,” he said.

Israel’s ambassador to Washington, Michael Herzog, described Jenin over the past two years as “a major hub of terrorism and an Iranian stronghold,” apparently a reference to reports by Israeli officials of Iran-backed Palestinian militant groups such as Islamic Jihad and Hamas flooding the area with weapons. He said many attacks on Israelis had originated from Jenin.

“No nation would sit idly by as terrorists strike its citizens,” Mr. Herzog wrote on Twitter after the start of the operation.

A week ago, a rocket was launched toward an Israeli community from the Jenin area but exploded soon after it took off, according to the military and video footage. While militant groups in the Palestinian coastal territory of Gaza have been launching rockets into Israel for more than 20 years, groups in the West Bank have not yet developed the same capabilities.

An Israeli military operation in Jenin on June 19 turned deadly, with at least five Palestinians killed in a gun battle and dozens more wounded, according to Palestinian health officials. One of those killed was a 15-year-old girl.

Eight members of the Israeli security forces were also wounded in the fighting that day, which broke out after a raid to arrest two Palestinians suspected of terrorist activity turned into lengthy exchanges of fire, according to the Israeli military.

Israeli helicopter gunships were sent into the area for the first time in decades to aid forces trying to extricate armored vehicles that had been disabled by a roadside bomb. Israeli analysts said that the roadside bomb was reminiscent of the kind that Israeli forces encountered in past decades in southern Lebanon.

Western-backed security forces belonging to the Palestinian Authority have largely stayed out of the hotbeds of militancy in the northern West Bank of late. Their absence, analysts say, suggests that they have lost control and left a power vacuum.

Members of the coalition government in Israel led by Prime Minister Benjamin Netanyahu — the most right-wing in the country’s history — have been pressing for a more aggressive military response to attacks on Israelis.

But the operation on Monday appeared to have broad support, as the leader of the opposition, the centrist Yair Lapid, voiced his backing for it.

“This is a justified step against a terror infrastructure based on accurate and high-quality intelligence,” he wrote on Twitter.

Raja Abdulrahim, Gabby Sobelman and Myra Noveck contributed reporting.