Gunmen have kidnapped six forestry surveyors in the violence-stricken southern Philippines, the military said Sunday, the latest in a number of attacks against environmental workers there in recent years.

The six were en route to study a government forestry programme in a remote mountainous area of Compostela Valley on the island of Mindanao when they were snatched Friday, the military said.

No one has claimed responsibility for the abduction, although various armed groups are known to operate in the area, including communist guerrillas and private security personnel who work for illegal loggers and miners.

"Our concern is the safe release of the civilians," regional military spokesman Lieutenant General Rainier Cruz said, as he deployed troops to help local police track down the victims, who work for the Department of Environment and Natural Resources.

At least 20 forest rangers have been killed since the government imposed a nation-wide logging ban to combat widespread illegal logging in 2010.

The rangers are often poorly equipped and up against illegal loggers backed by a private armed unit and sometimes corrupt local officials, the department has said.