The New Philippine Defence Secretary resigned yesterday in a dispute over the appointment of a retired general to be presidential adviser on national security.
Mr Orlando Mercado told a news conference he resigned because he did not agree with the appointment of a former armed forces chief, Mr Lisandrot Abadia, to the key security position.
The new President, Ms Gloria Macapagal Arroyo, said she had not accepted the resignation.
Mr Mercado said he would continue to support the Arroyo government but asked: "How can I serve the cabinet together with the national security adviser? We're supposed to be a team.
"I reiterate my recognition of the legitimacy of the Arroyo administration and I will personally oppose any attempts to destabilise or undermine its authority through adventurism and extra-constitutional means," he said in a statement.
Mr Mercado played a key role in last week's popular uprising against the former president, Mr Joseph Estrada, when he and the armed forces chief, Gen Angelo Reyes, withdrew their support from Mr Estrada and joined Ms Arroyo in a rally by hundreds of thousands of protesters demanding Mr Estrada's resignation.
Meanwhile, Ms Arroyo denied rumours of a coup by Lieut Gen Edgardao Espinosa and asked him openly at a press conference: "Are you trying to stage a coup against me?"
Ms Arroyo dismissed the question of whether Gen Espinosa, a senior officer in the Marine Corps, was unhappy with the new administration, saying: "He's an old friend of mine. Did he say he would stage a coup? I'll call him up right now."
A few minutes later, an aide handed Ms Arroyo a mobile phone with the general apparently on the other end of the line.
In full view of the cameras and scores of reporters, Ms Arroyo asked Mr Espinosa if he was plotting against her.