Police will summon 31 people, including actress Preechaya "Ice" Phongthananikorn, next week to acknowledge charges that they allegedly purchased cyanide illegally.

The Department of Industrial Works (DIW) has filed reports with the Crime Suppression Division against 31 people who are believed to have traded and purchased cyanide illegally, deputy national police chief Pol Gen Surachate Hakparn said.

They include Ms Preechaya and the alleged serial killer Sararat "Aem Cyanide" Rangsiwuthaporn, who is accused of murdering 14 people.

Ms Preechaya was said to have bought cyanide from the same source as Ms Sararat to use as a pesticide.

Charges related to the purchase of a chemical compound (cyanide) for wrongful use carry a maximum sentence of three years and a fine of up to 300,000 baht, or both, Pol Gen Surachate said.

In June, Pol Gen Surachate said Ms Sararat faces more than 75 charges -- including premeditated murder, attempted murder, theft causing death and forgery in 15 cases dating from 2015 to this year.

The 15 cases were spread over seven provinces -- Nakhon Pathom, Samut Sakhon, Kanchanaburi, Phetchaburi, Ratchaburi, Udon Thani and Mukdahan.

Police ended the investigation into Ms Sararat after questioning more than 900 witnesses over three months, he added.