LOS ANGELES (Updated, 8:23 a.m.) — Floyd Mayweather Jr. blamed Manny Pacquiao for the collapse of their prospective bout on Thursday, claiming the Filipino boxer refuses to accept a reasonable compromise on drug testing concerns.

Mayweather also says he's still ready to sign a deal for the fight, which was slated for March 13 at the MGM Grand Garden in Las Vegas before Pacquiao promoter Top Rank declared it dead on Wednesday.

Mayweather (40-0, 25 KOs) made his first public comments about the negotiations in a written statement that began with Mayweather saying he's "thoroughly disgusted" by Pacquiao's representatives' attempts to blame him for the collapse of what's likely to be the richest bout in boxing history.

"In my opinion it is Manny Pacquiao and his team who are denying the people a chance to see the biggest fight ever," Mayweather said. "I know the people will see through their smokes screens and lies. I am ready to fight and sign the contract. Manny needs to stop making his excuses, step up and fight."

The sides went to mediation on Tuesday in Santa Monica in an attempt to resolve the drug testing issues that are the only remaining conflicts in the negotiation. Mayweather's demands for frequent blood testing beyond the Nevada Athletic Commission's requirements — and Pacquiao's reluctance to agree to those requests — have derailed the bout.

Mayweather initially demanded repeated blood testing right up to the day of the fight, while Pacquiao asked for a 30-day cutoff before the bout. Mayweather now claims he agreed to a 14-day cutoff compromise before the mediation session began, but Pacquiao still wouldn't accept those terms.

"The truth is he just doesn't want to take the tests," Mayweather said.

Pacquiao has filed a lawsuit alleging Mayweather and most of his representatives, including Golden Boy Promotions CEO Richard Schaefer, defamed him by falsely accusing him of using performance-enhancing drugs.

Top Rank boss Bob Arum was brutally frank about his former fighter on Wednesday, telling The Associated Press that Mayweather is "a psychological coward who doesn't want to fight anybody who has a chance of beating him."

After generating stellar pay-per-view revenue from their previous fights, both Pacquiao and Mayweather likely stood to make much more than $25 million apiece from their welterweight bout. Mayweather returned to the ring after a 21-month absence in September with a victory over Juan Manuel Marquez, while Pacquiao (50-3-2, 38 KOs) pounded Miguel Cotto in November for his 13th straight victory since 2005.

Pacquiao is widely considered boxing's pound-for-pound champion, an unofficial title held by Mayweather before his aborted retirement. Their proposed fight was seen as the biggest moment in boxing since Mayweather's split-decision victory over Oscar De La Hoya in May 2007.

Daniel Weinstein, the retired federal judge who oversaw the mediation, also issued a statement on Thursday saying little about the actual discussions.

"In the end, the parties could not agree on a testing protocol acceptable to all," Weinstein's statement read. (AP)