Chris Brown was involved in an all-out brawl with Frank Ocean Sunday night, and sources connected with Chris  insist Ocean started it.

Chris was at Westlake Studio in the L.A. area listening to  one  of the artists he  represents. The sources say as Chris went to leave, Frank  Ocean and his crew blocked Chris from leaving. The sources say Frank said, "This is my studio,  this is my parking spot."

We're told Chris went to shake Frank's hand ... and that's when  one of Frank's people attacked Chris. Sources  connected with Chris say one of Chris' friends jumped in front and hit  Frank's friend.

Sources connected with Chris say Frank then  came at Chris ... Chris pushed him away and they  started brawling.

The police were called...

UPDATE 10:45PM PT: Police have cleared the scene. We're told Chris Brown was not there when officers arrived -- but they did speak to Frank Ocean. At this point ... we're told no one wants to press charges, and no arrests have been made.

UPDATE 3:00 AM PT:  Cops  say they  will continue to investigate and want to speak with Chris  Brown. They  refer to Ocean as "the victim" because  he's the one who stuck around and spoke with police.  Ocean said the fight started over a parking space (how L.A.) and Brown punched him.  There were 6 people involved  in the fight.

According to the Associated  Press:

Grammy-winning singer Chris Brown is under investigation for an alleged  assault in a West Hollywood parking lot, the Los Angeles County Sheriff's Department said  early Monday.

Frank took to Twitter, saying:

Chris doesn't have control of his Twitter account after several Twitter rants, but he does control his Instagram, which he took to after the fight, posting the following picture with the caption, "Working on my album. Not working on negativity. Focus on feeding ya family. Bullshit will forever be in the shadows."