Apple has revealed that it is working on a fix for an issue some are having with iOS 7. There have been complaints that since the new operation software arrived for iPhones and iPads a fault can occasionally occur when sending iMessages.

Some owners have taken to Twitter and Apple's own support forums to complain that sometimes an iMessage can look like it has been sent correctly but later appears with a red exclamation mark next to it that says it didn't go after all. And this can happen even when the user has a strong internet connection.

Read: iOS 7 tips and tricks: Here's what your iPhone or iPad can do now

The user can then send it as a normal SMS message, but that can cost a network rate and the original failure might not be noticed until much later.

Many are claiming that this started to happen to them after the 7.0.2 update.

Apple has responded to the complaints, admitting that a very small number of people are experiencing this issue and that it is looking into the problem.

"We are aware of an issue that affects a fraction of a percent of our iMessage users, and we will have a fix available in an upcoming software update," it said in a statement.

In the meantime, users recommend that restarting the phone fixes the problem for short periods. But it does return.