More than 100,000 packets of sliced bread have been recalled in Japan after parts of a black rat's body were discovered inside two of them, the manufacturer said Wednesday.

Food recalls are rare in Japan, a country with famously high standards of sanitation, and Pasco Shikishima Corporation said it was investigating how the rodent remains had crept in to its products.

The company said it was so far unaware of anyone falling sick after eating its processed white "chojuku" bread, long a staple of Japanese breakfast tables.

Around 104,000 packs of the bread have been recalled in mainland Japan, from Tokyo to the northern Aomori region.

"We would like to apologise deeply for causing trouble to our customers and clients," the company said in a statement on Tuesday.

Then on Wednesday, Pasco confirmed that parts of a black rat had contaminated the two packs.

They were produced by the breadmaker at a factory in Tokyo, whose assembly line has been suspended pending its probe, Pasco said.

"We will strengthen our quality management system to ensure there won't be a recurrence," it added.

Cleanness and hygiene are taken seriously in Japan, but food poisonings and recalls occasionally make headlines.

Last year, convenience store chain 7-Eleven apologised and announced recalls after a cockroach was found in a rice ball.

The latest health scare scandal in Japan was over the recall by drugmaker Kobayashi Pharmaceutical of dietary supplements meant to lower cholesterol.

The firm said last month it was probing five deaths potentially linked to the products containing red yeast rice, or "beni koji".