K ompong Seila, Koh Kong - Khmer Rouge attacks on Route 4 have been blamed on government soldiers cutting off business links with the rebels.
"Last year the [Royal Cambodian Armed Forces] soldiers deployed here worked with the Khmer Rouge to do logging and few attacks occurred along the road," said police commander Chhouk Ang.
"Now all links with the Khmer Rouge have been cut off...and that has angered them."
Col Ang - whose police forces have been guarding a segment of the road near Kampong Seila, about 130km southwest of Phnom Penh, since February - said there had been two KR attacks in the past four months.
He believed the KR in the area were growing increasingly hostile as their supply lines, and contacts with government forces, were clamped down on.
He alleged that, previously, RCAF soldiers used to go into KR-controlled areas, just 10-15km from the road, to be "partners" in the logging trade.
Some 90 KR guerrillas are believed to be stationed near the roadside village of Kampong Seila, continuing to threaten the security of Route 4, which connects Phnom Penh with Sihanoukville.
One person was killed and three injured when the KR attacked government forces along the road on June 12. A taxi and two Shell Oil trucks came under fire.
Government troop reinforcements have been sent to the area, which had earlier been protected by poorly-equipped policemen.
"The Khmer Rouge can attack us or ambush taxis at any time they want," said Col Ang, commander of police unit 911, on June 20.
The KR soldiers - based 10km west of Kampong Seila - numbered only about 90 but were heavily armed, he said.
"I have 330 policemen guarding the road but there is only one gun for every three of them. We have no arms and ammunition to push them out of the area."
The KR guerrillas were well-equipped with AK47 rifles, B40 grenade launchers, mortars and heavy machine guns.
"My police forces alone can not protect security along the road...I need more troops or a special mobile force to help my men, and ammunition is really needed."
The KR soldiers, believed to be from Divisions 18 and 19 in Koh Kong and Division 20 in Kampong Speu, attacked and briefly captured key police positions in Kampong Seila on June 12.
"The rebel troops came from the west side with vehicles carrying DK 82mm mortars and 12.7mm machine guns and hundreds of rounds were fired," he said.
He said the KR did not usually have such weapons, and alleged they had been provided by Thai businessmen trading with the rebels. The KR moved into Kampong Seila village, plundering 500kg of rice from villagers and burning down four sawmills.
Col Ang said a villager was killed, a policeman seriously wounded, and three KR later killed in counter-attacks by government forces. A taxi and two Shell Oil trucks which passed through the village at the time came under fire.
He said initial reports that a passenger in a taxi was shot were wrong, but both truck drivers were shot. "The guerrillas were not attempting to ambush the taxi and the trucks," Col Ang said.
"They were attempting to attack police positions and Kampong Seila village to get supplies."
A Shell Oil spokeswoman said one of the drivers, Khieu Kimsia, was shot in the knee, thigh and shoulder. Currently in a Phnom Penh hospital, he faced several months of treatment. She was unable to provide details about an assistant driver, also shot, who was in Sihanoukville Hospital.
Shell Oil said its trucks were still plying Route 4, transporting oil from Sihanoukville port, but their drivers remained worried about security.
