A US judge refused to toss out a verdict ordering Samsung to pay $1 billion to Apple for patent infringement, but reversed a finding of "willful" violations which could have tripled the award.

US District Judge Lucy Koh, in a mixed ruling issued late Tuesday, denied the South Korean electronic giant's request for a new trial.

"The trial was fairly conducted, with uniform time limits and rules of evidence applied to both sides. A new trial would be contrary to the interests of justice," she wrote.

But the California judge reversed the part of the original August 24 verdict that said the infringement was "willful," effectively preventing Apple from seeking even more compensation.

She wrote in her 40-page ruling that the evidence in the trial failed to "show by clear and convincing evidence" that Samsung made its devices knowing they infringed on Apple's patents for the iPhone and other Apple devices.

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. The charges were denied by Samsung.

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.

The case is among several pending in courts around the world in a battle between the two tech titans over patents. Two separate rulings by courts in Japan and the Netherlands have dismissed Apple's claims of patent infringement.

The dispute has major implications for the highly competitive smartphone market, of which Samsung has captured 29 percent compared to Apple's 21.8 percent, according to research firm IDC.

But Apple, which has seen its share price slide on fears of slowing growth, may be more concerned about the Google Android operating system used by Samsung and others.

A survey by Strategy Analytics said Android grabbed 70 percent of the global market in the final three months of the year.