ANCHORAGE, Alaska-- Authorities in Alaska's largest city say three first-graders have been disciplined over a plot to kill a fellow student with silica gel packets that the girls believed was poison.

Parents of the 32 first-graders attending Winterberry Charter School in Anchorage got word of the plot in an email Tuesday. School district officials say the students acknowledged they planned the poisoning.

CBS affiliate KTVA reported that the incident was first brought to a teacher's attention on March 22, according to ASD spokeswoman Heidi Embley. She said a student overheard three others discussing their plan to use silica gel -- a substance commonly found in product packaging -- to poison another classmate.

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"Given such a young age, it's not clear if they knew what they were doing, if it was just a threat or something more serious," she said.

Police say a school resource officer interviewed the girls and charges won't be filed. Silica gel packets, which soak up moisture, aren't poisonous.

"Student safety is the top priority in the Anchorage School District and we take all threats to student safety very seriously," Embley said Tuesday, adding that she had not heard of any similar incidents in her time with the school district.

Discipline was left up to the school district. The email says it entailed "significant consequences." Embley says she couldn't release further details.

Police say the plot emerged from an ongoing feud.

Principal Shanna Mall told Anchorage television station KTUU that the students were suspended. Mall couldn't immediately be reached for comment Wednesday.