SAN FRANCISCO (AFP) - A US judge has upheld a ruling against Samsung in its long legal battle with Apple, maintaining that South Korean firm owes more than US$1 billion (S$1.2 billion) in damages to its US rival and denying a request for a new trial.

However, the US District judge in California reversed the part of the original Aug 24, 2012 verdict that said the infringement was "willful," effectively preventing Apple from seeking even more compensation.

Apple had accused Samsung of illegally copying parts of its popular iPhone and iPad for the South Korean electronics giant's flagship Galaxy line of smartphones and tablets, charges denied by Samsung.

The damages awarded in August could have been tripled over the jury's finding that Samsung's infringement had been "willful," but Judge Lucy Koh reversed that part of the ruling, saying Samsung had a "reasonable defence." Neither Apple nor Samsung could immediately be reached to comment on the ruling, which was published Tuesday in a 40-page court document.

Samsung had appealed the original ruling, depicting the verdict as a loss for consumers and contending that Apple had "manipulated" the patent system in order to go after its Galaxy S smartphones.

Two separate rulings by courts in Japan and the Netherlands have dismissed Apple's claims of patent infringement.

The legal dispute between the two tech giants has major implications for the highly competitive smartphone market, of which Samsung has captured 29 per cent compared to Apple's 21.8 per cent, according to research firm IDC.