MANILA: Manny Pacquiao on Thursday accepted US rival Floyd Mayweather's provocative challenge for a showdown of the world's top pound-for-pound boxers, though sticking points to the mega fight remain.

The unbeaten Mayweather dared the Philippine icon this week on Twitter to "Step up Punk", attempting to entice Pacquiao into a May 5 bout in Las Vegas, a fight that boxing fans have wanted to see for years.

Mayweather and Pacquiao, 33, previously saw a fight derailed by the US fighter's demands about blood testing, with both boxers accusing the other of running scared.

"I want to fight him. This is the fight the world wants," Pacquiao declared at a news conference in the Philippines with his US promoter Bob Arum.

Pacquiao, 54-3 with two draws and 38 knockouts, said if the 34-year-old Mayweather, 42-0 with 26 knockouts, can find a promoter who would give him a guaranteed purse, the fight would be on.

Arum said he favours a showdown in late May and previously told the Los Angeles Times he could secure $40 million more with the construction of a temporary venue in Las Vegas before more than twice as many spectators.

"Mayweather wants a guaranteed purse so what he has to do is get a promoter who can give him the guarantee," Pacquiao said. "I don't have problems getting a guarantee because I have a promoter who will give me my guaranteed purse."

"If he gets a guarantee, then we are going to share the revenue on a 50-50 basis," Pacquiao added, referring to the money raised from pay-per-view television, gate and broadcast rights.

Arum added: "There is no problem on our part -- the problem is on Mayweather's."

Mayweather needs somebody on his side that's going to guarantee his purse. Mayweather has nobody on his side and GBP (Oscar de la Hoya's Golden Boy Promotions) is not going to guarantee his purse."

Arum insisted that if there was to be no fight in late May against the American then he would move forward with a Pacquiao clash on June 9 against someone else.

He listed a re-match against Mexico's Juan Manuel Marquez or Puerto Rican southpaw Miguel Cotto, as well as Americans Tim Bradley and Lamont Peterson, as potential alternatives.

Arum had originally said that Mayweather was not on Pacquiao's hit-list.

Pacquiao, a southpaw, won a majority decision over Marquez in November to keep his World Boxing Organisation welterweight title.

Mayweather, who turns 35 next month, won the World Boxing Council welterweight title with a fourth-round knockout of compatriot Victor Ortiz.

But he is currently awaiting the June 1 start of a 90-day jail sentence on domestic violence charges, further complicating things.