Philippine President Rodrigo Duterte lifted Saturday night his unilateral declaration of ceasefire with the leftist rebels and ordered the security forces to be "on high alert."

In a statement released at 7:00 p.m. local time, Duterte said: "Let me now announce that I am hereby ordering the immediate lifting of the unilateral ceasefire that I ordered on July 25 against the communist rebels."

On July 25, Duterte declared the unilateral ceasefire with the communist rebels, voicing the hope that the rebels will reciprocate to his peace offer.

"To immediately stop violence on the ground, restore peace in the communities and provide an enabling environment conducive to the resumption of peace negotiations, I am announcing a unilateral ceasefire with the Communist Party of the Philippines, the New People's Army and the National Democratic Front effective immediately," Duterte said during his first State of the Nation Address.

The President withdrew the truce declaration after the Communist Party of the Philippines-New People's Army-National Democratic Front (CPP-NPA-NDF) failed to meet his ultimatum for the rebels to reciprocate the truce until 5:00 p.m. local time Saturday.

He issued the ultimatum after the rebels ambushed a group of paramilitary in southern province of Davao del Norte two days after he declared the unilateral suspension of offensive military operations during his first State of the Nation Address.

A militiaman was killed and four others were wounded in the attack.

With the lifting of the unilateral truce, Duterte ordered the Armed Forces of the Philippines and the Philippine National Police to also withdraw the operational guidelines they issued in pursuance to the ceasefire declaration.

"I am ordering all security forces to be on high alert and continue to discharge their normal functions and mandate to neutralize all threats to national security, protect the citizenry , enforce the laws and maintain peace in the land," he said.

The Philippine military said the NPA has an estimated 4,000 members. The rebels have been fighting the government since 1969 in one of Asia's longest-running insurgencies.

The government has been trying to forge peace with the leftist rebels since 1986 but the on-off talks have faltered many times in the past.

Government officials said as of the moment, the formal peace talks in Oslo, Norway on August 20-27 between the government and the rebel group will push through despite the lifting of the ceasefire.