Junior middleweight contender Tim Tszyu is standing firm on his demand for a mandatory crack at WBC, IBF, WBO, WBA undisputed world champion Jermell Charlo.

Tszyu was ringside last Saturday night in Los Angeles, to watch Charlo score a tenth round knockout of Brian Castano to unify all four of major sanctioning titles.

The Australian star is the WBO's mandatory challenger. He now wants to pressure the sanctioning body to order the fight.

Tszyu recently made his United States debut with a big points win over Olympian Terrell Gausha.

After his big undisputed fight was over, Charlo was questioned, by an Australian reporter, about the possibility of facing Tszyu - and he fired off 'F--- you and Tim Kazoo! Change the mic.'

Tszyu explains that there is legitimate animosity between the two and feels the event would have a good build.

"He’s a very disrespectful man, so stuff him. I don’t like him anyway," Tszyu told Fox Sports.

"I think me and him will sell because there’s no love between us two – it’s all hate. If you want a dance partner, I’m here. I’m here to try to take you out. If you want to punch on I’m always keen. I’m the mandatory challenger. He has a few months to make a decision or he vacates the belt. Fight me or vacate – that’s all there is."

George Rose of No Limit, who promote Tszyu, said negotiations were already taking place for a fight with Charlo in Los Angeles.

"I love that [Charlo and his team] pretend they don’t know Tim but when [Charlo] says that Tim doesn’t deserve to fight him he’s saying that because he doesn’t want to fight him - Tim is the most dangerous guy in the super welterweight division," Rose said.

However, Charlo has two other mandatory defenses at his door - with Sebastian Fundora for the WBA and Bakhram Murtazaliev for the WBC. It's not clear which of the three mandatories will come first, but Murtazaliev has been waiting for the longest period of time.