New Delhi, June 29 -- Blistering heat and strong winds Sunday stoked wildfires across the West after three firefighters were killed a day earlier in Colorado while battling a blaze along the state's border with Utah.

The National Weather Service said wildfire conditions "remain critical" across the Southwest, with risk high in the Four Corners region where Arizona, Colorado, New Mexico and Utah intersect. The agency warned of "extreme fire behavior" along the Utah-Colorado border, where "rapid fire growth is likely."

The firefighters were killed and two sustained burn injuries when they were overcome Saturday by flames from fast-moving fires. They deployed emergency protective shelters during the so-called burnover - which occurs when a...