Investigative sources say a man arrested after allegedly throwing what appeared to be Molotov cocktails in front of the headquarters of Japan's main ruling party was wearing protective gear at the time of the incident.

The police believe the suspect carefully prepared and are investigating his motive and other details.

On Saturday morning, the man approached the Liberal Democratic Party's headquarters in a van and threw the objects.

He subsequently drove on and crashed the van into fencing around the Prime Minister's Office, roughly 500 meters away from the first scene.

Tokyo police arrested 49-year-old Usuda Atsunobu on suspicion of throwing an apparent smoke bomb toward a police officer guarding the prime minister's office.

Investigators say the man sprayed liquid of some sort in front of the LDP building, apparently using a high-pressure cleaning machine. Three riot police officers complained of sore throats and other symptoms. Investigative sources say the suspect was in protective gear, including a mask.

Investigators also found that unused Molotov cocktails left inside the car contained mixtures of gasoline, alcohol and other substances. It also found that each bottle had two fire starters that were fixed with adhesive taping.

Police say the man is currently remaining silent about the allegations.