In a nation governed by one of the world’s most draconian anti-cannabis laws, it’s rare enough to stumble upon marijuana plants thriving on the side of a road.

Imagine the surprise, then, when a crop of marijuana was found earlier this week in what is perhaps one of the unlikeliest places of all: Nagatacho, home to Japan’s political elites. In a highly rare case, Tokyo Metropolitan Government staff on Thursday confirmed — and then removed — four marijuana plants sprouting on the premises of an office building for Upper House lawmakers, according to Masahiro Hirai, an official with the health and welfare bureau of the metropolitan government.

A few hours before the removal, the bureau had received a call from an AERA dot journalist — who later broke the story — notifying it of the existence of what appeared to be marijuana plants near the building, Hirai said. The bureau swiftly dispatched two of its staff members to dispose of them.

Isao Morishita, an Upper House employee in charge of administrative issues, said he didn’t recall any similar incidents having been reported at the building in the past, although no official records would exist.

The marijuana plants discovered Thursday seemed about one or two months old, but plants can appear to be more or less mature than they really are depending on the amount of sunlight to which they were exposed and the fertility of the soil surrounding them, Hirai said.

At the moment there is no way to confirm whether the plants appeared naturally or were being raised by someone. The Tokyo bureau is not ruling out any possibility, but it believes “the probability is higher that the plants were just growing naturally,” the official said, adding that it’s not entirely impossible that marijuana seeds landed there after being carried by the wind or being eaten and then defecated by birds. But such cases are rather rare, especially given Japan’s stringent anti-cannabis law prohibiting the unlicensed cultivation of marijuana.

Under the law, those found to have illegally cultivated or possessed marijuana are subject to imprisonment for up to seven years or five years, respectively. “Because of our strict license system regarding marijuana cultivation, it’s not like the seeds fly around and sprout constantly,” Hirai said.

According to the metropolitan government there were four cases of marijuana removal in fiscal 2017 in Tokyo, involving a total of 44 plants.

“At this point, we can’t completely deny that someone was deliberately trying to cultivate marijuana there, so we’re looking into that possibility, too,” he said.

While the Canadian Senate passed a bill earlier this week paving the way for the historic legalization of recreational marijuana use, the drug remains deeply stigmatized in Japan.

Japan’s decades-old cannabis law even forbids the medicinal use of marijuana “by anyone,” subjecting violators to up to five years behind bars.

In some European countries and more than 20 states and provinces in the U.S., medicinal use of marijuana is legalized.

In Japan only those with a license are allowed to cultivate marijuana. Health ministry data shows there were 33 recognized growers across the nation in 2014.