Almost 100 pig-tailed macaques raided a polling station at a Phichit temple in Muang district Sunday and tore down voter lists for the referendum on the draft charter.
Police previously arrested two 8-year-old girls for election sabotage. Children also were interrogated in Rayong province.
Police were alerted Sunday morning about the macaque incident at an open hall of Wat Hat Mun Krabue.
Pol Lt Col Banchob Uthayo, an investigator of tambon Yanyao police station, other investigators from the station and Chatchawan Suksawat, Moo 1 village headman of tambon Yanyao of Muang district, had arrived at the scene.
Lists of eligible voters and referendum-related announcement papers put up at the polling station were found to have been destroyed.
Five out of 15 voter list papers had been ripped, along with seven out of 10 papers detailing the referendum vote. The damaged papers were collected for examination.
Villagers told police that almost 100 macaques living around the temple stormed the polling station and tore down the documents there.
Election officials also detained and charged two high school students who tore down voter lists in what they thought was a clean-up.
The two students "confessed" to tearing down three lists of eligible voters for the charter referendum attached to a notice board at a polling station in Rayong's Klaeng district.
They were among four students playing in the area on Friday. The four were questioned by police to determine whether they were hired by someone to rip the documents. Klaeng district chief Wittaya Chapanon also attended the session.
The two students told police there was no one behind their acts, adding they thought these were old documents.
They were sent to Rayong juvenile court to face prosecution.
Two eight-year-old girls have been legally charged under the draconian law for tearing down voter lists, police said Saturday. Foreign reports described the focus on election sabotage as "increasingly bizarre".
The French news agency AFP reported Saturday on the arrest of the children, saying the junta has outlawed most discussion and criticism of its draft charter, which may be voted upon at a referendum currently scheduled for Aug 7. A special law provides a prison sentence of up to 10 years for illegal rhetoric or writing.
Campaigning of any kind is also banned and authorities have already arrested or warned scores of people for handing out critical leaflets or wearing "Vote No" T-shirts.
The eight-year-olds fell foul of the law after "confessing" to tearing down voter lists outside a school in Kamphaeng Phet province because they liked the paper's pink colour.
The pair have been officially charged under the Referendum Act with "obstructing the referendum process, destroying official documents and destroying common public property", said Damrong Phetpong, the police commander of the province.
They will not face jail time as the law exempts anyone under the age of 10 from criminal punishment, he said.
He actually defended the police action, claiming the force were duty-bound to file the charges.
"Police have a duty to compile witnesses and evidence and then refer the case to a public prosecutor" who will decide whether to pursue the case, he told AFP.
The junta has become increasingly jittery ahead of the poll, with police initially speculating that anti-junta activists were behind the torn voter lists.
But an investigation led officers to the girls, who were questioned at a police station.
The junta opened monitoring centres across the country this month and is on high alert to block any movement against the charter from supporters of the ousted government, who are expected to vote against it, the AFP report said.
Last week, the National Broadcasting and Telecommunications Commission (NBTC) exercised its new censorship powers under Section 44 to shut down Peace TV, the red shirts' a critical satellite TV station.