Almost 20,000 people have been forced from their homes in the southern Philippines by fighting between government forces and gunmen associated with Muslim rebels, officials said Wednesday. At least 50 gunmen were surrounded by the military in a remote marsh area of Mindanao island, as eight days of violence there and on nearby Basilan island left 37 soldiers, police and civilians dead. Dozens of gunmen occupied several schools in the marsh area at the weekend, forcing thousands of residents to flee as soldiers and police descended on the zone backed by air strikes. More than 11,500 people have fled their homes in the remote Zamboanga Sibugay region of Mindanao, said local disaster relief chief Adriano Fuego, while the gunmen have pushed deeper into the marshes. "We do not know if the situation might escalate. There is also the fear that other groups might join in. There are always sightings (of armed men) in other areas," he told AFP. Although the military said the gunmen have been penned in, the suspects could be reinforced and spread the fighting elsewhere, Fuego added. The government has accused the gunmen of killing four soldiers and four policemen in ambushes there last week as well as for previous kidnappings. The gunmen were initially identified as members of the country's main Muslim rebel group, the Moro Islamic Liberation Front, but the MILF disowned them on Tuesday. However the MILF has claimed responsibility for the killing of 19 special forces commandos last week after they strayed into rebel territory on adjacent Basilan in a separate incident. More than 7,800 Basilan villagers have taken refuge in government evacuation centres due to fears that the military would attack the MILF, said regional civil defence head Ramon Santos. However Santos said the tension in that area had subsided as troops were withdrawn and replaced by local police. Residents of Basilan, also the home of various armed groups, are frequently displaced by outbursts of violence usually linked to the decades-old MILF rebellion, he added. "They are not panicked. This is not the first time so they know what to do. They are quite prepared mentally, even the children, we looked at them and there was no trauma. Life goes on," he told AFP. The violence has cast a shadow over the government's peace talks with the MILF, which began in 2003 and includes a ceasefire. President Benigno Aquino said on Monday that the peace process would continue, a stand later echoed by the 12,000-strong MILF.