A court on Tuesday convicted a Japanese man of landing a drone containing a bottle of radioactive sand from Fukushima on the roof of Prime Minister Shinzo Abe's office.

The Tokyo District Court handed Yasuo Yamamoto, 41, a two-year jail term, suspended for four years, for forcibly obstructing the operation of Abe's office.

Though convicted, the sentence means Yamamoto will avoid prison time so long as he stays out of trouble for the next four years.

Yamamoto has admitted flying the drone last April, but his defence denied the charge and argued that it was his way of expressing his opposition to the use of nuclear power, Jiji Press reported.

The unemployed Yamamoto sent the drone with the contaminated sand on April 9 and it sat on the roof until found on April 22.

A blog, reportedly by Yamamoto, chronicled how sand from Fukushima -- where nuclear reactors went into meltdown after the March 2011 earthquake and tsunami -- was placed in the bottle with a card also attached to the drone voicing opposition to atomic energy.

Traces of radiation were detected but were reportedly too low to be a risk to human health.

The case prompted wider public discussions on rules for drones, with the government setting tighter regulations for flying unmanned objects in urban and densely populated areas as well as places around airports.