Bemused followers of Japan's foreign minister were left scratching their heads on Tuesday after a bizarre tweet about bacon, sparking tongue-in-cheek speculation he could be tweeting classified information in code.

"Ah, bacon is in fact ^%?$+*o!%...." Taro Kono tweeted in Japanese from his verified account to his 513,000 followers, prompting confusion and many times the number of retweets and "likes" he usually gets from more orthodox tweets about diplomatic meetings.

On Sunday he tweeted his son had greeted him by "screaming bacon with all his might" when he returned home in the early hours.

"What does he want to do?" he tweeted, uploading an image of a sheet of paper on which someone had written the word "bacon" in Japanese.

Ministry officials were tight-lipped. "We are not in a position to say as it's his own Twitter account," a foreign ministry spokesperson said.