MANILA (REUTERS) - After Philippine President Rodrigo Duterte said that Emmanuel "Manny" Pacquiao should name corrupt government offices, the boxer-turned-lawmaker expressed his disappointment on Tuesday (June 29).

In a statement, Mr Pacquiao said he accepted Mr Duterte's challenge, but said it was disheartening that they were fighting over the issue of corruption.

"I had mistakes in life that I corrected but I can hold on to two things: I am not corrupt and a liar," Mr Pacquiao said on Tuesday.

The comments were the latest chapter in a surprise war of words between the President and Mr Pacquiao, who is seen as being among his strongest backers and a possible successor when the single six-year term he is allowed expires next June.

The firebrand Philippine leader said Mr Pacquiao had criticised corruption in his government and threatened to expose the boxing champion as a liar.

"I'm not saying there is no corruption, so expose it," Mr Duterte said in a televised late night national address. "If you don't do that, I will expose you daily as a liar... I know you from way back."

Using an expletive in his strongest language yet against Mr Pacquiao, Mr Duterte said if he did not reveal corruption, he would be "playing politics".

Mr Pacquiao, 42, has long been among Mr Duterte's strongest supporters, backing his bloody war on drugs and bid to reintroduce the death penalty. The eight-division champion has yet to announce his presidential bid.

Early this month, Mr Duterte criticised Mr Pacquiao's "shallow" foreign policy knowledge, after the senator said he found the leader's stand on the South China Sea "lacking" and "disheartening".

Mr Duterte remains popular in the Philippines. Political allies are urging him to run as vice-president when his term ends. His daughter Sara - a long-term aide - is also seen among his possible successors.