KFC said that more than 700 of its 900 UK-wide chicken shops had been forced to close since the weekend, while others were offering a downsized menu or shorter opening hours.
"We've brought a new delivery partner onboard, but they've had a couple of teething problems -- getting fresh chicken out to 900 restaurants across the country is pretty complex," KFC said in a statement.
"We won't compromise on quality, so no deliveries has meant some of our restaurants are closed, and others are operating a limited menu, or shortened hours.
"We know that this might have inconvenienced some of you over the last few days, and disappointed you when you wanted your fried chicken fix -- we're really sorry about that," the company added.
DHL said in a separate statement that it was working to resolve the problem.