President Rodrigo Duterte has sacked his interior secretary, as corruption allegations and infighting rock his government.

Mr Ismael Sueno, who led a volunteers' group that campaigned for Mr Duterte, was fired at the end of a Cabinet meeting on Monday night.

He is the second secretary to be forced out of the Cabinet, after former foreign secretary Perfecto Yasay, since Mr Duterte took office less than a year ago.

"It was basically... a loss of trust and confidence in the man and the position," Mr Duterte's spokesman Ernesto Abella told a news briefing yesterday.

Mr Sueno, 69, was fired after three of his deputies, also appointees of Mr Duterte, accused him of using government money to build a new hotel, expand his farm and buy new trucks for his rice trading business.

They also alleged that he cleared the purchase of 76 firetrucks at 20 million pesos (S$557,000) each, when there was another offer for just seven million pesos apiece.

Mr Abella said Mr Duterte "checked into the matter, and apparently has taken note of several legally untenable situations".

Mr Sueno later issued a statement saying: "I respect the president's decision, but I am not corrupt."

He said the three deputies were resentful because he had clipped their powers. Mr Sueno said the hotel is owned by his brother, and the trucks were paid for by his daughter, who runs the family business. The firetrucks deal was already signed before he took over, and he found nothing irregular with the price, he added.

Mr Duterte has already removed dozens of bureaucrats, two senior immigration officials and a former campaign spokesman from their positions in connection with graft.

Infighting within the government is also slowing the President's efforts to deliver on his campaign promises.

Finance Secretary Carlos Dominguez has criticised Environment Secretary Gina Lopez for shutting down 23 mines and scrapping over 70 mining contracts.

In Congress, House Speaker Pantaleon Alvarez and Representative Antonio Floirendo, both long-time friends of President Duterte, have been publicly feuding over a spat involving their girlfriends.

Senator Antonio Trillanes, a vocal critic of Mr Duterte, said Mr Sueno's sacking was just a "convenient excuse" to appoint a preferred politician to the key post, suggesting it may be former senator Ferdinand Marcos Jr, the son and namesake of the late Philippine dictator.

Mr Duterte has been vocal about his political debt to the Marcos family.

Representative Ruffy Biazon said the President "showed remarkable political will", but that "the dismissal should have been accompanied by an explanation of the reason and basis for the loss of confidence".

As interior secretary, Mr Sueno oversaw Mr Duterte's anti-narcotics drive that has left over 7,000 suspects dead, killed either by the police, vigilantes, or in gang purges.

In February, he helped organise a pro-Duterte rally, which more than 200,000 people attended, to counter a mass protest denouncing the killings.