Philippine officials say the country's top diplomat, who was behind a bold government move to challenge the validity of China's vast territorial claims in the South China Sea before an international tribunal, has resigned due to health reasons.

Presidential spokesman Herminio Coloma Jr. said Monday that President Benigno Aquino III has accepted Foreign Secretary Albert del Rosario's resignation, which will take effect on March 7.

The 76-year-old del Rosario has been an outspoken critic in the Association of Southeast Asian Nations of China's increasingly assertive stance in disputed waters.

Coloma did not cite a reason for del Rosario's resignation, but two senior diplomats say del Rosario has been suffering from a spinal problem and a heart ailment that prompted doctors to recently implant a pacemaker to regulate his heartbeat.