FILE PHOTO: KitKat chocolates are pictured in a shop at Nestle headquarters in Vevey, Switzerland, February 15, 2018. REUTERS/Denis Balibouse/File Photo

LUXEMBOURG (Reuters) - A legal adviser to the European Union's top court advised judges on Thursday to reject an appeal by Nestle NESN.S in defense of its EU trademark for its KitKat chocolate wafer biscuit.

In the latest twist of a decade-long legal battle between the Swiss food giant and its U.S. rival Mondelez MDLZ.O, Advocate General Melchior Wathelet advised the European Court of Justice to uphold a lower court ruling which found that public recognition across Europe of the shape of the four-fingered bar was not enough to merit the KitKat trademark granted in 2006.

Wathelet also called an appeal by Mondelez against a part of the lower General Court’s findings to be “manifestly inadmissible” because the U.S. firm’s overall complaint against the Nestle trademark had been successful.

ECJ justices generally follow such advice when giving their rulings several months later, although not always. A decision by the Court of Justice will be final.

Duelling between the two companies has also seen Nestle challenge Mondelez’s British trademark for the shade of purple wrapper on its Cadbury’s Daily Milk chocolate bars.