Apple said demand for the device, which was first unveiled in January but only became available in the US on April 3, was far higher than expected.
"Demand is far higher than we predicted and will likely continue to exceed our supply over the next several weeks as more people see and touch an iPad," Apple said in a statement.
"Faced with this surprisingly strong US demand, we have made the difficult decision to postpone the international launch of iPad by one month, until the end of May."
Apple said it would reveal the UK pricing for the iPad and start taking pre-orders for the device on May 10.
"We know that many international customers waiting to buy an iPad will be disappointed by this news, but we hope they will be pleased to learn the reason-the iPad is a runaway success in the US thus far.
Initially April said the iPad would launch in the UK at the end of April, although the company hadn't provided a specific date.