Investigators were trying to determine whether frost heaves contributed to the rupture of an interstate natural gas pipeline in Warren, Minn., Marshall County Sheriff John Novacek said Tuesday.

The accident, which caused a massive fire, happened shortly after 6 a.m. Monday on the Viking Pipeline in northwestern Minnesota, cutting off natural gas service to 900 customers in Warren and Argyle. No one was injured in the accident, which happened in a farm field about a mile from the nearest house.

Novacek said 10 evacuated families have returned to their homes on farms in the vicinity, and gas service may be restored in the two cities by Wednesday. He said one business, Melody’s Cafe in Warren, remained closed, unable to operate without hot water.

Minnesota Office of Pipeline Safety investigators were on the scene Tuesday, trying to determine the cause.

Novacek said investigators have ruled out suspicious activity because there were no tracks in the mud. He said the last cleaning of a nearby drainage ditch was in 2002, ruling out digging as a possible cause.

Natural damage such as frost heaving causes about 7 percent of U.S. pipeline accidents, according to the Pipeline Safety Trust, a nonprofit based in Bellingham, Wash., that has tracked pipeline safety issues ever since a deadly 1999 accident in that city. Pipeline companies are required to conduct integrity tests on pipelines under federal requirements imposed after that and other accidents.

In January, the rupture and fire on a natural gas transmission line in Canada caused Xcel Energy to ask customers to lower thermostats to 60 degrees to conserve energy for two days during a disruption in supply.

In Warren on Tuesday, contractors were on site to make repairs, said Brad Borror, spokesman for Tulsa, Okla.-based ONEOK Inc., parent company of Viking Gas Transmission Co., which operates the line that runs across Minnesota to Marshfield, Wis.

Novacek said workers were taking out the damaged portion of the line Tuesday, and planned to bury the new pipe deeper, eliminating an existing bend. Borror, in an e-mail, said the company submitted its repair plan to regulators, but could not say when the pipeline flow would be restored.

The pipeline fire burned for about 1½ hours Monday after Viking shut off the gas. The fire was visible from Hwy. 75, causing such a traffic jam that the State Patrol was called out, Novacek said.