A half-dozen Regional School Unit 71 buses were taken off the road on Wednesday after a surprise inspection by Maine State Police troopers, who deemed the vehicles "unsafe to drive."

The buses were inspected by the district mechanic and received passing inspection stickers a week ago, according to a NewsCenter Maine report.

A letter from Superintendent Mary Alice McLean posted on the district website said after-school activities were cancelled Wednesday and bus routes have been temporarily consolidated. Students affected by the changes live in the communities of Searsmont, Belmont, Morrill and Swanville, she wrote.

McLean went on to say in her letter, "As superintendent of schools I am conducting a thorough investigation into the reasons behind the buses' removal from circulation and the inspection sticker irregularity, as well putting forth a plan for structural changes in the areas of transportation and maintenance in our school district.

"The safety of our all of students is my highest priority as well as the the timely and reliable transportation of students to and from school and school activities."

The inspection issue is the second bus-related problem in the district in recent months .In January, Nickerson school in Swanville closed for a day because the district did not have enough substitute drivers to cover the daily bus routes.

A phone message left for McLean seeking additional information has not been returned.

This story will be updated as information becomes available.