Four members of the Philippine presidential guard were wounded in a firefight with dozens of Maoist rebels disguised as soldiers at a checkpoint on the southern island of Mindanao, the military said on Wednesday, Reuters reported.
The attack on the elite Presidential Security Group (PSG) in North Cotabato province will be a another blow to a stuttering peace process between the government and National Democratic Front, the political arm of the communist rebels.
President Rodrigo Duterte was not in the region.
"Four of our troops in two vehicles were slightly wounded in the firefight," PSG commander Brigadier-General Louie Dagoy told reporters, adding that the rebels fled.
Dagoy said the New People's Army (NPA) guerillas opened fire on the presidential guards and were wearing soldiers' uniforms.
The peace process has been fraught with breakdowns and allegations of breaches of unilateral ceasefires by the military and the NPA.
Informal talks in the Netherlands are due to take place at the weekend to restart stalled negotiations to end the nearly 50 years of conflict, which has killed more than 40,000 people.
The encounter at the checkpoint came a day after Duterte requested both houses of Congress to extend martial law in Mindanao until the end of the year as security forces needed more time to deal with Islamist militants.
Duterte on Tuesday met his peace negotiators and instructed them not to agree to any bilateral ceasefire until the NPA ceased attacks on government troops and called on the Maoists' political leaders to keep their fighters under control.
The latest incident highlights the challenge facing a military stretched on multiple fronts in Mindanao, an island of 22 million people with a long history of rebellion.
Government forces are battling to defeat Islamic State-allied rebels who have occupied the heart of Marawi City for 58 days, while operations continue on islands in the west of Mindanao against heavily armed Abu Sayyaf bandits behind kidnappings and piracy.
The presidential guard unit is usually deployed ahead of activities by the president to secure areas in advance. Dagoy said the PSG was carrying out other work and not preparing for a visit by Duterte.
Police and military officials said the attack did not appear to be targeted as the unit were traveling in civilian clothes in unmarked vehicles.