The latest fire severely damaged Beaverton Freewill Baptist Church in northwest Alabama, near the Mississippi state line.
The white, wood-frame church sat about 150 yards off a two-lane county road and had an alarm system that alerted officials to the blaze.
"It's definitely arson," state fire marshal spokesman Ragan Ingram said Sunday.
Fire marshals are investigating whether the Saturday afternoon blaze was linked to the other nine, all of which were set in the pre-dawn hours this month. Gov. Bob Riley said last week that the nine earlier church fires appear linked.
A federal investigator said witness reports and behavioral profilers led authorities to believe that two white men were responsible for the fires.
Witnesses said they saw two men in a sport utility vehicle near a number of the fires.
"They're not youths or teens. It's probably someone in their 20s or 30s. We believe they're pretty much inseparable. They're something like bosom buddies," said Eric Kehn, a spokesman for the federal Alcohol, Tobacco, Firearms and Explosives agency. The ATF is the government agency with authority in cases of arson.
Evidence from one of the earlier fires indicates the perpetrators may have been briefly trapped inside the building and may have been hurt, said Jim Cavanaugh, ATF regional director.
Investigators have said they don't know of a motive, but there is no racial pattern. Five of the churches had white congregations and five black.
All were Baptist, the dominant faith in the region, and were mostly in isolated country settings.