A shooting at a mosque complex in California killed three people, with two suspected teenage gunmen later found dead in a car from self-inflicted gunshot wounds, police said.
Police said emergency response teams found the victims outside the sprawling Islamic Center of San Diego, before later finding the shooters, aged 19 and 17, also dead.
TV footage from a helicopter showed armed response teams gathered outside a building, with one unidentified person lying in a pool of blood.
"We are actively investigating this as a hate crime," San Diego Police Chief Scott Wahl told reporters.
"There was definitely hate rhetoric that was involved."
The Islamic Center is described on its website as the largest mosque in San Diego county, which lies in southern California.
After a short period of lockdown when authorities advised residents to stay inside, San Diego police announced that the threat at the center had been "neutralised."
"We received a call of an active shooter at the Islamic Center. Within four minutes, officers arrived on scene and observed immediately three deceased victims out in front," Mr Wahl said.
"We immediately began to deploy with an active shooter response into the mosque and adjacent school," he said, adding that police had received calls about more gunfire nearby, where a landscaper had been shot at but not hit.
Place of worship targeted
A few blocks from the Islamic center, police found a vehicle in the middle of the street with the shooters dead inside.
"The suspects at this point appear to have died from self-inflicted gunshot wounds. There were no officers involved in firing their weapons," Mr Wahl said.
He said that a security guard at the Islamic center was among the three victims killed and his actions had helped prevent a deadlier attack.
"His actions were heroic and he undoubtedly saved lives today," Mr Wahl said.
The identities of the other two fatalities were not immediately clear.
Mr Wahl said that the mother of one of the suspects had contacted police two hours before the attack and reported that her son was "suicidal" and that several weapons and her vehicle were missing.
Initially, police deployed to an area around a high school which the suspect was associated with, until they received a call of an active shooter at the Islamic Center.
The imam at the mosque, Taha Hassane, said that all the staff, teachers and children at the mosque were safe.
"We have never experienced tragedy like this before. And at this moment all that I can say is, sending our prayers and standing in solidarity with all the families in our community here," he said.
"It is extremely outrageous to target a place of worship," the imam added.
US President Donald Trump described the shooting as a "terrible situation".
"I've been given some early updates, but we're going to be going back and looking at it very strongly," he told reporters.
Wahl, the police chief, said that given the location of the attack, investigators were "considering this a hate crime until it's not."
State Governor Gavin Newsom expressed horror at the attack, saying: "Worshippers anywhere should not have to fear for their lives."
"Hate has no place in California, and we will not tolerate acts of terror or intimidation against communities of faith," he said on X, adding, "To the San Diego Muslim community: California stands with you."
