Apple has been denied a trademark for the popular iPad Mini by the US Patent and Trademark Office.

The trademark application for the tablet was turned down because the name was "merely descriptive" and did not create a unique meaning, it said.

But Apple still has until July to persuade the Patent Office that the smaller tablet differs sufficiently from its iconic sibling.

Apple has been involved in a series of patent disputes with rival firms.

It won a landmark case against Korea's Samsung last year but this month, a judge in the US ordered the $1bn (£660m) in damages awarded to Apple be cut by 40% and set a new trial to assess the level of damages.

The award was the biggest in a series of global legal fights between the two companies over patents.

The Patent Office issued the letter in January, although it has only just emerged.

In it, it said the "applied-for mark merely describes a feature or characteristic of applicant's goods".

The terms "mini" and "pad" and the prefix "i-" were all descriptive, it decided.

Neither as individual terms nor as a composite result - iPad Mini - did they "create a unique, incongruous, or non-descriptive meaning in relation to the goods being small handheld mobile devices comprising tablet computers capable of providing internet access".

In its last quarter to January, Apple said that it sold a record 22.9 million iPads and iPad Minis.