A fire that engulfed 10 tents at a south Minneapolis homeless encampment Monday afternoon and hospitalized one was ignited by an unattended propane heater, fire officials said Tuesday.

The cause was ruled accidental.

Firefighters responded to the blaze at Hiawatha Avenue and 26th Street around 3:15 p.m. and extinguished the 4-foot-tall flames using fire retardant. No serious injuries were reported, but one woman at the encampment was taken to the hospital for smoke inhalation.

The fire — and frigid weather — is likely to increase pressure on city, county and American Indian officials to expedite efforts to relocate the encampment, which appeared this summer and has become the home of nearly 200 adults and children. A temporary shelter, planned for a nearby Red Lake Nation-owned site, is scheduled to open in mid-December.

With the sudden onset of freezing weather last week, city officials had expressed concern that improvised heating equipment might cause fires or carbon monoxide poisoning at the camp.

“We found out today that these tents burn very quickly,” Minneapolis Fire Chief John Fruetel said Monday.

“We are urging everyone to please, please take advantage of the shelter that’s been offered,” he said.