 -- Two mosques were attacked by vandals in the same Southern California town -- incidents that authorities are investigating as possible hate crimes, police said.

Police in Hawthorne, California, responded on Sunday morning to a report of vandalism and a possible explosive device in front of the Ahmadiyya Muslim Community Baitus-Salaam Mosque, said the Hawthorne Police Department, whose detectives are leading the investigation.

Officers found graffiti on a fence saying "Jesus," as well as what "appeared to be a hand-grenade type of device in the driveway," said police.

The area was evacuated and the LA County Sheriff's Bomb Squad responded.

It was later determined that the device "was a plastic replica of a hand-grenade," police said.

Separately, the police department was called about vandalism at the Islamic Center of Hawthorne, where the front of the building was spray-painted with the phrase, "Jesus is the way," Hawthorne police said Sunday.

Both incidents appear to have occurred overnight, police said, and both incidents are being classified as possible hate crimes. The FBI's LA Field Office is also investigating, police said.

Jawdat Dajani, president of the board of directors at the Islamic Center of Hawthorne, told ABC News he believes the vandalism was in response to an inter-faith "walk-and-rally" held Saturday by the clergies of Hawthorne's St. Joseph Catholic Church and the Islamic Center of Hawthorne. The Hawthorne police chief, city and civic leaders, and over 200 parishioners participated, the Hawthorne police said.

"I feel bad because ... the day before, we had a walk for peace and healing," Dajani told ABC News.

"That same night ... somebody came," he said. "Somebody who saw what happened and didn't like what happened, and wanted to express his anger."

The center's members were notified of the vandalism, said Dajani, adding that everyone's reactions seemed calm. Dajani said he expects acts like vandalism, but doesn't want to make a "big deal" out of it and make situations "tenser than they are."

The Ahmadiyya Muslim Community Baitus-Salaam Mosque could not be immediately reached by ABC News for comment, but Ahsan Khan, a chapter president of the community, said, according to the Associated Press, "This type of behavior is born out of ignorance and fear and we as members of the Ahmadiyya Muslim Community ... we respond with peaceful dialogue." "It's through peaceful dialogue that we can hopefully see less of this type of hate crime," Khan said, according to the AP.

The FBI said that "investigators will work to identify the person or group responsible, the motivation and whether religious bias was a factor."

"All evidence will be reviewed by state and federal prosecutors to determine whether a violation under federal civil rights statutes occurred," the FBI's statement said.

The Hawthorne police said that staff from its Community Affairs Unit are "working in closer dialogue with our area Islamic faith centers ever since the tragic events occurring in San Bernardino."

"The Department will continue to closely support our faith-based partners and work to assure the safety of its members," the police said.

Just days before these mosque attacks in Hawthorne, a fire was reported at the Islamic Society of Palm Springs in Coachella, California. Carl James Dial, 23, was arrested in connection with the fire. Dial faces five felony charges including arson, commission of a hate crime and second-degree burglary, according to arrest records.