Japan's Burger King has taken their black burger series to a new height, adding black cheese and black sauce to their popular black buns.

The fast food chain initially launched the Premium Kuro Burger (kuro means "black") in 2012, colouring the bread with bamboo charcoal and adding squid ink to the ketchup.

In 2013, the series upgraded to the Kuro Ninja, which kept the buns and squid ink ketchup and added on a slice of bacon.

Now Burger King, from Sept 19, will sell two more black burgers - the Kuro Pearl priced at 480 yen (S$5.67) and the Kuro Diamond at 690 yen (S$8.15).

Both burgers feature the signature black buns, bamboo charcoal cheese, beef burgers made with black pepper and an onion and garlic sauce with squid ink.