Samsung says it will appeal against a US court ruling that the South Korean giant stole designs from Apple to make smartphones and computer tablets.
The jury in San Jose, California ordered Samsung to pay Apple $1.05bn (£665m) in damages.
In response, Samsung accused Apple of using US patent laws to try to dominate the smartphone market.
Analysts say the ruling is one of the most significant in a global battle over intellectual property.
In recent weeks, a court in South Korea ruled that both technology firms had copied each other, while a British court threw out claims by the US company that Samsung had infringed its copyright.
But the year-long US case has involved some of the biggest damages claims.
Samsung described Friday's decision as "a loss for the American consumer".
"It will lead to fewer choices, less innovation, and potentially higher prices," the firm said.
The statement added that it was "unfortunate that patent law can be manipulated to give one company a monopoly over rectangles with rounded corners".
Apple, however, said it applauded the court "for finding Samsung's behaviour wilful and for sending a loud and clear message that stealing isn't right".
It said it intended to seek injunctions to block US sales of Samsung products at a follow-up hearing on 20 September
The two firms account for more than half of global smartphone and tablet computer sales.
The nine-person jury at the federal court in San Jose, California had to consider 700 questions about each side's claim that its rival had infringed its intellectual property.
It deliberated for less than three days before coming to a unanimous decision, rejecting all of Samsung's claims and upholding five of Apple's allegations, including:
- Some of Samsung's handsets, including its Galaxy S 4G model, infringed Apple's design patents for the look of its iPhone including the system it uses to display text and icons
- All the disputed Samsung devices had copied Apple's "bounce-back response", which makes lists jump back as if yanked by a rubber band
- Several Samsung devices incorporated Apple's facility allowing users to zoom into text with a tap of a finger
Apple had wanted $2.5bn in damages. Samsung had sought $519m.
It may also seek to use this ruling to block other devices powered by Google's Android software that it believes replicate elements of its user-interface, including current models by Samsung as well as other firms.