The 20-acre cannabis plantation was no secret.

The farm, near Mandalay in central Myanmar, had been praised on Facebook by a group calling itself the Mahar Legalization Movement Myanmar, which wants the Burmese government to ease the heavy penalties it imposes on cannabis production and use.

The group approvingly posted photos of what it called an “industrial hemp plantation” run by foreigners — just the sort of agriculture it said the country needed. The post was viewed thousands of times on Facebook.

Among those viewers were the Myanmar police, who took a decidedly less-sanguine view. This week, a day after the post went up on Facebook, they arrested three people, including an American, accusing them of running an illegal marijuana operation.

The American, John Fredric Todoroki, 63, is being held along with two Burmese citizens, U Shein Latt, 37, and Ma Shun Le Myat Noe, 23. They were detained in the township of Ngazun. The police were still searching for another American, Alexander Skemp Todoroki, 49. It was unclear how the two Todorokis are related.