Two teenage gunmen opened fire Monday at the Islamic Center of San Diego, killing three men before taking their own lives a few blocks away, according to The Associated Press.

San Diego Police Chief Scott Wahl said a security guard at the Islamic Center was among those killed. Authorities said the guard's actions were heroic and helped prevent the attack from becoming worse.

The shooting happened while children were at the center's school, but police said the students were safe. The Islamic Center is the largest mosque in San Diego County, according to its website.

Police said the case is being investigated as a hate crime. Wahl said there was "hate rhetoric" involved, though authorities had not reported a specific prior threat against the Islamic Center.

For Santee and East County residents, the attack is a countywide public safety story, especially for families connected to schools, places of worship and community centers. Authorities said the investigation is continuing.