The killings Monday at San Diego’s largest mosque are being investigated as a hate crime, touching off concerns about rising Islamophobia in the United States.

“Islamophobia endangers Muslim communities across this country,” Zohran Mamdani, New York City’s first Muslim mayor, said in response to the shooting, which left three people dead, in addition to the two shooters. “We must confront it directly and stand together against the politics of fear and division.”

Islamophobia has been an intractable problem in the United States for decades. Hate crimes against Muslims surged following the Sept. 11, 2001, attacks, according to F.B.I. data.

More recently, the war in Gaza, which set off protests across American college campuses, has contributed to a steady increase in anti-Muslim sentiment and inspired violence against a range of religious institutions, including synagogues and churches. Antisemitic incidents also skyrocketed following the start of the conflict in 2023, according to the Anti-Defamation League.

The Council on American-Islamic Relations received 8,683 civil rights complaints in 2025, the most the group has recorded since 1996, according to its most recent report.

“Government actions and official rhetoric treated Muslims — and people who speak up for Palestinian human rights — as suspicious and outside the circle of protected religious and civic life,” the council wrote in the 2025 report.

In recent months, attackers have targeted individuals and community centers.

Following the Oct. 7 attacks in Israel, a landlord killed a 6-year-old Palestinian American boy and stabbed his mother, who survived.

During the federal immigration crackdown in Minnesota, a lone assailant assaulted Representative Ilhan Omar at a news conference. The congresswoman, who is a prominent Somali American Muslim and outspoken critic of the president, was unharmed.

Before the enforcement operation, President Trump had likened the Somali community in Minneapolis to “garbage.”

In February, a shooting occurred at the Islamic Center in Matamoras, Pa., during the holy month of Ramadan. No one was inside the center at the time of the shooting, but the bullets destroyed windows and furniture.

On Jan. 30, a woman was charged with attacking three people, including punching a 12-year-old wearing a hijab in the face, in the heavily Muslim neighborhood of Bay Ridge in Brooklyn.

On Monday, at a news conference only hours after the shooting in San Diego, Taha Hassane, an imam at the Islamic Center, spoke of his shock and grief.

“It is extremely outrageous to target a place of worship,” he said. “People come to the Islamic center to pray, to celebrate, to learn, not only Muslims, but we have people from all walks of life.”