The MILFs news website, luwaran.com, said retired Gen. Ramon Santos, chairman of the governments ceasefire committee, and his MILF counterpart, Von Al Haq, and Ampatuan signed the agreement.
MILF rebels in Shariff Aguak, Mamasapano and Datu Unsay towns battled it out with militiamen and civilian volunteers loyal to Ampatuan from June 28 to July 6, sparked by the deadly June 23 roadside bombing in Shariff Aguak which left seven people dead.
Maj. Gen. Rodolfo Obaniana of the Armys 6th Infantry Division and Malaysian Gen. Pahlawan Soheimi, chief of the 60-member international monitoring team, also signed the low-level agreement, according to luwaran.com.
The international monitoring team, composed of 60 soldiers and policemen from Malaysia, Brunei and Libya, has been helping enforce the ceasefire between the Armed Forces and the MILF for the past three years.
The agreement was reached six days after Presidential Assistant for Mindanao Jesus Dureza brokered an informal "suspension of hostile actions" by the Moro rebels and the militiamen.
The hostilities have displaced some 16,000 people, mostly marginalized Maguindanaons relying on farming for livelihood.
The agreement outlined measures to prevent renewed hostilities in the three municipalities.
The joint ceasefire committee and the provincial government agreed to establish monitoring posts manned by soldiers and unarmed MILF representatives who would observe, on a round-the-clock basis, the demilitarized areas surrounding the war-torn villages.
MILF fighters residing in areas protected by the "buffer zones" will be barred by the ceasefire monitors from carrying their firearms when they roam around.
To prevent undue hostilities, the military and the MILF should first coordinate with the monitoring posts before carrying out any tactical maneuvers in areas covered by the low-level security agreement.
The activities of MILF fighters in areas near the "buffer zones" will also be monitored.
Col. Franklin del Prado, spokesman of the Armys 6th Infantry Division, said all of their units in Shariff Aguak, Datu Unsay and Mamasapano towns have been told to cooperate to normalize the situation in the three areas.
Government troops were not involved in the hostilities between the MILF rebels and militiamen.