Washington/Los Angeles, Nov 8 (PTI) A US Marine veteran dressed in black sprayed bullets inside a crowded dance bar popular with college students Wednesday night, killing at least 12 people, including a police officer, in Thousand Oaks city in California, in one of the "horrific" mass shooting incidents in the US.

The gunman, who also injured nearly two dozen others, was found dead inside the Borderline Bar and Grill on the outskirts of Los Angeles.

Ventura County Sheriff Geoff Dean identified the gunman as 28-year-old Ian David Long, a retired Marine who served in Afghanistan. The suspect used a .45 caliber Glock handgun during the shooting, Dean said.

Long, who shot himself, was dead when officers made entry into the bar, Dean said as he described the shooting incident as "horrific."

"It's a horrific scene in there, there is blood everywhere and the suspect is part of that," he said.

He said the motive of the shooter is still unclear. He was known to authorities for minor crimes.

The shooter was on active duty with the US Marine Corps from August 2008 to March 2013, according to Department of Defense records. He also served in Afghanistan from November 2010 to June 2011.

Authorities had "minor" run-ins with Long in the past, Dean said, citing few incidents.

"We have had several contacts with Long over the years, minor events, a traffic collision," Dean said, adding that deputies were called to his house for a disturbance in April this year and "felt he might be suffering from Post-traumatic stress disorder (PTSD)."

Twenty-one people wounded in the shooting were treated and released from area hospitals, according to the Ventura County Sheriff's Office.

President Donald Trump said that he has been "fully briefed on the terrible shooting in California."

"Law Enforcement and First Responders, together with the FBI, are on scene. 13 people, at this time, have been reported dead. Likewise, the shooter is dead, along with the first police officer to enter the bar....

"Great bravery shown by police. California Highway Patrol was on scene within 3 minutes, with first officer to enter shot numerous times. That Sheriff's Sergeant died in the hospital. God bless all of the victims and families of the victims. Thank you to Law Enforcement," Trump said in a series of tweets.

In memory of victims, President Trump in a proclamation ordered that the flag of the US shall be flown at half-staff at the White House and upon all public buildings and grounds.

The hooded gunman burst into the bar around 11:20 p.m. (local time) entirely dressed in black.

Ventura County Sheriff's Department Sgt. Ron Helus and a California Highway Patrol officer entered the bar first and were met with gunfire from the suspect, the Los Angeles Times reported, citing officials.

Helus was shot several times and succumbed to his injuries at a hospital.

He was planning to retire next year after a 29-year stint with the sheriff's department, Dean said.

Helus, who died "a hero", is survived by a son and his wife, whom he called before entering the bar, Dean added.

It was the second mass shooting in the US within two weeks.

"We have no idea if there is a terrorism link to this or not. As you know, these are ongoing investigations and that information will come out as soon as we are able to determine exactly who the suspect was and what motive he might have had for this horrific event," Dean added.

The Marine Corps extended its "deepest condolences to the families of the victims in this senseless tragedy."

Citing witnesses, the paper said that people ran for cover when shooting started. Some people tried to break windows using chairs to escape the building while some hid in bathrooms.

The FBI's Joint Terrorism Task Force has been rushed to the scene, according to an agency spokeswoman. Representatives from the US Bureau of Alcohol, Tobacco, Firearms & Explosives were also dispatched.

According to bar's website, Wednesday nights are college-themed nights open to students as young as 18.

Quoting witnesses, the paper said the event is popular with Moorpark college students, and the Pepperdine student newspaper tweeted that students from its campus were also inside at the time of the shooting.

"He just pulled out a gun and shot my friend that was working the front desk," 21-year-old Holden Harrah was quoted as saying by the paper.

"I heard more gunshots behind me. I was freaking out," said Harrah, who was among the hundreds inside listening to music Wednesday night as a part of the college night event.

The suspect is reported to have drove his mother's car to the attack and said nothing upon entering the bar.

Authorities are searching his home and the weapon used for the crime.

This is the second time this year Thousand Oaks has seen violence in a crowded area. In March, a man shot and killed his wife before attempting to shoot himself at the Thousand Oaks Mall, the paper added.

Last week, a gunman opened fire at a Jewish synagogue in the US city of Pittsburgh, killing 11 people and injuring several others including three policemen, in the deadliest "anti-Semitic attack" in America in years.

(This is an unedited and auto-generated story from Syndicated News feed, LatestLY Staff may not have modified or edited the content body)