Los Angeles  - Two Jewish men were shot outside a synagogue Thursday in Los Angeles, prompting police to go on high alert to protect Jewish groups throughout the city.

Authorities were careful to avoid terming the attack a hate crime, pending further inquiry. Police detained a suspect soon after the incident but released him several hours later after he cooperated with the investigation.

Both victims were shot in the legs as they parked separate cars in a garage under the synagogue and headed for the door leading to the worship area, Deputy Police Chief Michael Moore said in broadcast remarks.

The two victims were hospitalized in stable condition.

The Adat Yeshurun synagogue is located in North Hollywood, an area of Los Angeles separate from the Hollywood of film fame, and home to a large Jewish community.

Police said they had issued the alert to other Jewish groups in case the attack was part of a wider anti-Semitic campaign.

"These are the times in which we live," Moore said. "What we are going to assume is that there is potential for this to escalate."

"We're going to assume that this synagogue did play a role in this, and (it's a) reasonable expectation that we alert our other friends in the Jewish community and increase their vigilance," he said.

Speaking to reporters outside the taped-off synagogue, Los Angeles Mayor Antonio Villaraigosa tried to temper worries that the shooting was a hate crime.

"None of us should presume or speculate more about this other than it was a random act of violence," he said.

The suspect had been described as a black male wearing a hooded sweatshirt. Someone matching that description had been detained, Moore said. But the Los Angeles Times quoted police sources as saying it was doubtful he was the attacker.

The shooting came months after a shooting at the Holocaust Museum in Washington by an elderly white supremacist.

In 2006, a mentally ill gunman stormed into a Jewish centre in Seattle, Washington, killing a woman and wounding five others. In 1999, white supremacist Buford Furrow attacked a Jewish community centre about 16 kilometres from Thursday's assault, wounding three children, a teenager and an adult. (dpa)