President Rodrigo Duterte of the Philippines said on Monday that boxer-turned-lawmaker Emmanuel “Manny” Pacquiao should name corrupt government officials to show that he is not just politicking ahead of a presidential race next year.

The remarks were the latest in a surprising war of words between the president and Pacquiao, who is viewed as one of his most ardent supporters and a possible successor after his single six-year term finishes in June.

The flamboyant Pacquiao had attacked corruption in his government, according to the Philippine leader, who vowed to expose Pacquiao as a liar.

“I’m not saying there is no corruption, so expose it,” 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 Pacquiao, Duterte said if he did not reveal corruption, he would be “playing politics” and pledged to take action against any erring officials.

It was not immediately clear what officials he was urging Pacquiao to expose, or why. Pacquiao has not publicly been speaking about any allegations of high-level corruption in recent days.

Pacquiao, the acting president of Duterte’s political party, was not immediately available for comment outside office hours.

Pacquiao, 42, has long been one of Duterte’s most ardent fans, pledging his support for his violent drug war and bid to reinstate the death sentence. The eight-division champion has yet to declare his candidacy for president.

Duterte slammed Pacquiao’s “shallow” foreign policy understanding earlier this month, after the senator stated the leader’s stance on the South China Sea was “lacking” and “disheartening.”

In the Philippines, Duterte is still popular. When his tenure finishes, his political allies are pressing him to run for vice president. His daughter, a long-time aide, is also being considered as a prospective successor.