(USA TODAY) - Why did the chicken cross the road?

In the United Kingdom, the better question is why didn't the chicken cross the road?

The fast-food chain is engulfed in a crisis in the U.K., where about two-thirds of its restaurants are temporarily closed amid delivery challenges.

The cause? A chicken shortage.

Yes, a chicken shortage at a chicken place.

Trying to make light of the situation, KFC referenced the old-fashioned riddle joke in a tweet.

"The chicken crossed the road, just not to our restaurants," KFC's United Kingdom and Ireland outfit said on Twitter. "We've brought a new delivery partner onboard, but they've had a couple of teething problems — getting chicken out to 900 restaurants across the country is pretty complex!"

The chain promised not to "compromise on quality, so no deliveries has meant some of our restaurants are closed and others are operating a limited menu or shortened hours."

The brand has about 900 locations in the United Kingdom, and only about 300 were open as of Monday morning.

The situation was not expected to affect the U.S. market.

The exact cause of the delivery problems was not immediately clear, but the U.K.'s Guardian publication reported that KFC blamed the episode on delivery service DHL.

Spokespeople for U.S.-based Yum Brands, which owns KFC, were not immediately available to comment Monday.

DHL said in a statement: "Due to operational issues a number of deliveries in recent days have been incomplete or delayed. We are working with KFC and our partners to rectify the situation as a priority and apologize for any inconvenience this may have caused.”

KFC had 21,487 restaurants worldwide as of the end of 2017. Sales at U.K. KFC stores rose 5% in 2017.

Contributing: Kim Hjelmgaard

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.