Polygamist leader Warren Jeffs was in critical condition in a Texas hospital Monday after falling ill during a fast, a state prison official and his attorney said.

A source familiar with Jeff’s medical condition told CNN Monday that Jeffs was in a coma. The source did not provide further details.

The leader of the Fundamentalist Church of Jesus Christ of Latter-day Saints, a breakaway Mormon sect, was sentenced early this month to life in prison plus 20 years for sexual assault. Jason Clark, a spokesman for the Texas Department of Criminal Justice, said Jeffs was sent to a hospital in Tyler on Sunday night and was in critical but stable condition Monday.

“He was not eating or drinking enough fluids and also has some other medical conditions,” Clark told CNN. He would not elaborate, citing inmate privacy rules.

Jeffs told officials at the Powledge prison unit that he was not on a hunger strike, but had been “fasting,” Clark said. His attorney, Emily Detoto, confirmed Jeffs’ condition and that he had not been eating.

On August 4, Jeffs was found guilty of the aggravated sexual assaults of a 12-year-old girl and a 15-year-old girl he claimed were his “spiritual wives.” He will have to spend at least 45 years in prison before being eligible for release, state prosecutors said.

Jeffs was also found guilty of two counts of rape by accomplice in Utah in 2007 and was sentenced to 10 years to life in prison there.

His church is believed to have about 10,000 followers, and the practice of polygamy — which the mainstream Mormon Church renounced more than a century ago — is part of the sect’s doctrine.

CNN’s Gary Tuchman, Dave Alsup and Vivian Kuo contributed to this report.