Philippine authorities have arrested three men linked to a group that allegedly planned to set off firebombs at the Manila airport and a mall to protest the government's alleged "soft" stance in its territorial dispute with China.

Justice Secretary Leila de Lima said Tuesday that the alleged leader of the group and two other men were arrested Monday with four home-made incendiary devices found inside their car at the airport car park.

Government agents, who were tipped off by an informant, say the men planned to set off one bomb at a car park toilet and the three others inside one of the country's biggest malls.

The Philippines has filed diplomatic protests against alleged Chinese incursions into areas in the South China Sea claimed by Manila.