KFC's Zinger and Tower burgers, both of which contain a thick piece of chicken breast, are no longer available in most of its 140 outlets nationwide. The two sandwiches reportedly account for 15 percent of KFC's overall sales.

KFC said the discontinuation was mainly due to a supply shortage of large chickens after the bird-killing virus, avian influenza, broke out earlier this year. It said the fillet used for the popular burgers come from these larger chickens.

However, the supply of chicken breasts shrunk by 40 percent after the bird flu led to the killing of hundreds of thousands of chickens in farms across the country, according to industry experts, reports The Korea Times.

"We're running short on chicken fillets because a growing number of farmers, who can't afford soaring feed costs, are killing the birds before they grow big enough," said Kim Duk-bae of the Korea Poultry Association.

He explained that chicken feed costs have spiked almost 40 percent compared to last year, as a weakening won and the massive volatility in global commodity markets pumped up grain costs to record levels.

According to the poultry group, about 4,000 chickens are set to be slaughtered this month, which is about 500 less than in November last year.

He said supply would remain on edge through the first part of next year because grain costs aren't expected to moderate in the near future.

But does all of this mean that KFC, which prides itself as the world's most popular chicken chain, should shy away from selling its signature meal?

At least for now, says KFC's local representative, stressing, however, that it will try to resume sales sometime in December.

Till then, the company says it plans to offer drumsticks and introduce new non-chicken items to cater to consumers.