Philippine President Rodrigo Duterte has withdrawn a unilateral ceasefire with communist rebels after his ultimatum for the group to reciprocate lapsed. 

The Saturday deadline was set by Duterte after a rebel ambush in the southern island of Mindanao on Wednesday left one government militia member dead and four others wounded.

The recently elected president ordered on Saturday all government forces to go on high alert and "continue to discharge their normal functions and mandate to neutralise all threats to national security, protect the citizenry, enforce the laws and maintain peace in the land".

In a statement published in a government website, Duterte also told the police and the military to withdraw the ceasefire guidelines for their forces. 

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Duterte's decision marks an abrupt end to a four-day truce, which was seen as the first step in ending a decades-long armed campaign in the Philippines. 

It was during his first State of the Nation address on Monday, when Duterte declared a truce.

Two days later, however, rebels killed a government militiaman and wounded four others in Mindanao, angering Duterte, who gave the rebels until 07:00 GMT on Saturday to declare their own ceasefire.

In an interview with local television ABS-CBN, communist leader Jose Maria Sison said the rebels were planning to declare a ceasefire by 10:00 GMT, three hours after Duterte's deadline.

Filipino communist leader Jose Maria Sison has been living in exile in The Netherlands since 1987 [AP File Photo]

'Spurious ceasefire'

"The newly elected president is too volatile," Sison, speaking in Filipino, said from the Netherlands. "He can't just issue an ultimatum and expect the revolutionary group to immediately follow what he wants."

Sison called Duterte "stubborn" and someone who "lacks prudence" on a problem that has being going on for decades. 

In a separate statement, a rebel spokesman in southern Philippines said the ceasefire was "non-existent" in their area, because of continued military operation.  

Philippine President Duterte declares ceasefire with communists

Rigoberto Sanchez said the government "cannot burden" the rebel fighters from reciprocating "what is turning out to be a spurious unilateral ceasefire". 

On Friday, Luis Jalandoni, the chief rebel negotiator, had told Al Jazeera that the rebels would declare a truce "very soon". He also cautioned Duterte about issuing an ultimatum.

The rebels have been waging an armed rebellion to seize power since 1969 and tens of thousands of people have died in the conflict.

The military estimates the current strength of NPA, which is the armed wing of the NDFP, at about 4,000 fighters, significantly down from more than 26,000 at its peak in the late 1980s.

Duterte was swept to power in May on a wave of public anti-establishment frustration over crime and poverty, winning 16 million votes.

After becoming president, Duterte gave concessions to the rebels, naming left-wing activists to two Cabinet posts and moving to resume peace talks with them, starting on August 20 in the Norwegian capital of Oslo.

Both rebel leaders Sison and Jalandoni said that they still supported the upcoming talks, even as they called for the "immediate release" of some senior communist detainees.

Source: Al Jazeera and agencies