YUBA CITY, California (Reuters):

Teachers locked classroom doors, lowered shades and kept nearly 22,000 school children inside all day on Thursday in two northern California cities after a man threatened to go on a killing spree inspired by Monday's mass murder at Virginia Tech.

Police patrolled public schools in Yuba City and nearby Marysville 40 miles (64 km) north of state capital Sacramento after Jeffery Thomas Carney allegedly said he intended to make the mass slaying at Virginia Tech "look mild".

Virginia Tech student Cho Seung-Hui shot and killed 32 people and himself on the Blacksburg, Virginia, campus on Monday in the deadliest shooting rampage in modern U.S. history.

The murders have prompted a series of scares at universities and schools across the United States.

Local officials say Carney called his pastor at the United Methodist Church on Wednesday evening to say he was armed with an AK-47 rifle, improvised explosive devices and poison and would seek to provoke a confrontation with police to "commit suicide-by-cop."

"At about 8:30 a.m. we asked the principals to put all schools in lock-down," said Nancy Aaberg, superintendent of the 12,000 pupil Yuba City Unified School District. "We just kind of felt it was a consistent across-the-board safety measure."

"We actually had police at all of our campuses," she said in an interview. "It was a generic threat; there was no specific threat to any of our specific schools."

Yuba City Officials sent high school students home early. Officials in sister city Marysville across the river also locked down schools, impacting 9,700 students, an administrator said.