The attack at the Islamic Center of San Diego is being investigated as a hate crime, San Diego Police Chief Scott Wahl said at a news conference at a neighborhood park across from the mosque. The mosque is just east of Mission Bay, which is about 20 minutes north of downtown San Diego.
The initial call came in at 11:45 a.m., and officers responded within four minutes, Wahl said. As they arrived, gunshots rang out a few blocks away, where a landscaper was shot at but uninjured. The shooters were found dead in a vehicle stopped in the middle of a road nearby, he said.
Among those killed was a mosque security guard, who police believe "played a pivotal role" in keeping the attack from being "much worse," Wahl said. Families at the Islamic Center who knew the security guard said he was a father of eight.
The Islamic Center of San Diego identified the security guard as Amin Abdullah.
"This guy, like, it didn't matter who walked up, who came, any random person could just walk up. He would greet them, make sure they're OK," said a man who considered the security guard a friend.
Both suspects, ages 17 and 18, are dead from apparent self-inflicted gunshot wounds, police said. They have not yet been identified. Authorities initially said the suspects were 17 and 19, but in a later update, the San Diego Police Department clarified that they are 17 and 18 years old.
Heavily armed FBI agents were seen entering one of the suspect's home Monday night. They had guns drawn when they approached the door.
Two hours before the initial call came in, police said they received another call from a parent reporting a runaway juvenile. The teen's parent told police that several weapons from her home were missing, a vehicle was missing, and her son may have been suicidal. She said he was with another person, and they were dressed in camouflage.
That information triggered a police response, and police began using tools like license plate readers to track the vehicle around San Diego. Officers were sent to a mall in Fashion Valley and Madison High School, trying to zero in on the suspects.
Sources tell ABC News that anti-Islamic writings were found in the vehicle with the two teens. Search warrants are being executed at homes affiliated with the two suspects.
The center is the largest mosque in San Diego County and includes the Al Rashid School that offers courses in Arabic language, Islamic studies and the Quran for students ages 5 and up, according to its website.
"All of the kids are safe," Wahl said, appearing emotional. "Our hearts go out to the families that are in this moment being notified of what has happened to their loved ones."
Aerial TV footage showed more than a dozen children holding hands and being walked out of the parking lot of the center as it was surrounded by scores of police vehicles. The white mosque is in a neighborhood of homes, apartments and strip malls with Middle Eastern restaurants and markets.
Parents were directed to a nearby area to retrieve their children.
The mosque's director, Imam Taha Hassane, called it "extremely outrageous to target a place of worship."
"All the places of worship in our beautiful city should always be protected," he said.
He added that the center focused on interfaith relations and community building, and that a group of non-Muslims had been touring the mosque earlier Monday to learn about Islam.
The Council on American-Islamic Relations, one of the largest Muslim civil rights and advocacy groups in the U.S., condemned the shooting.
"No one should ever fear for their safety while attending prayers or studying at an elementary school," said CAIR-San Diego Executive Director Tazheen Nizam in a statement. "We are working to learn more about this incident and we encourage everyone to keep this community in your prayers."
Gov. Gavin Newsom's office said he was being briefed.
"We are grateful to the first responders on the scene working to protect the community and urge everyone to follow guidance from local authorities," his office posted on the social platform X.
Increased security at Islamic Center of Southern California
Police departments in major cities across the country are monitoring the situation. In Southern California, the Los Angeles Police Department said there's currently no known threat to L.A., but the department remains vigilant: "Out of an abundance of caution, we are providing extra patrols at mosques, Islamic centers, and all houses of worship across the City to ensure our communities are safe and feel supported."
In New York City, the NYPD said there's "no known nexus to NYC or specific threats to NYC houses of worship," but the department said it is increasing officer deployments to mosques "out of an abundance of caution."
The Chicago Police Department said in a statement that "while there is no actionable intelligence in Chicago, we are paying special attention to places of worship throughout the city out of an abundance of caution."
The Islamic Center's website says its mission is to not only serve the Muslim population but also "work with the larger community to serve the less fortunate, to educate, and to better our nation." Five daily prayers are held there, and the mosque works with other organizations and people of all faiths on social causes.
Julie Watson with the Associated Press and ABC News contributed to this report.