(CNN) -- — At least 158 people have been killed since fighting broke out between separatist rebels and soldiers in the Philippines, state news reported Wednesday.
The majority of those killed, 125, were militants from the Moro National Liberation Front (MNLF), the government-run Philippines News Agency (PNA) said. Also among the reported dead were 15 members of the military, five from police, and 13 civilians.
The crisis in Zamboanga City began when large numbers of rebels from the Muslim militant group came ashore this month.
The unrest has fueled fears of increased instability in a region where the central government is pursuing a new peace plan after decades of violence.
More than 109,000 people have been displaced in Zamboanga City and close to 19,000 are displaced in Basilan province, according to the United Nations, which described the situation Wednesday as a humanitarian crisis.
Zamboanga City, on the southwestern tip of Mindanao, is a mainly Christian city.
"We are increasingly alarmed by the situation and the growing needs of people caught up with violence," said Luiza Carvalho, U.N. resident and humanitarian coordinator in the Philippines. "We are particularly concerned for the most vulnerable, especially the well-being of women and children."
The rebels are a faction of the MNLF, a separatist movement founded in 1971 by Nur Misuari with the aim of establishing an autonomous region for Muslims in the mainly Catholic Philippines. The MNLF signed a peace deal with the central government in Manila in 1996, but some of its members have broken away to continue a violent campaign.
Last month, Misuari issued a "declaration of independence" for the Moro nation -- referring to Mindanao's indigenous Muslim population -- after complaining that the MNLF had been left out of a recent wealth-sharing agreement with another insurgent group, the Moro Islamic Liberation Front, which has fought for decades to set up an independent Islamic state on resource-rich Mindanao.