Montana-Dakota Utilities Co. is seeking approval from North Dakota regulators to raise residential electric bills by nearly $10 per month.

BISMARCK, N.D. (AP) — Montana-Dakota Utilities Co. is seeking approval from North Dakota regulators to raise residential electric bills by nearly $10 per month.

The Bismarck-based utility lists "significant" investment in facilities to maintain safe, reliable service as the reason for the request to the Public Service Commission.

MDU is proposing a 6.6 percent increase, which would raise an additional $13.4 million per year. It would increase a monthly residential bill by an average of about $9.60.

MDU serves about 100,000 customers in 117 North Dakota communities. The utility hasn't had a general electric rate increase for five years.