The US government has threatened to break up Google to end its illegal monopoly on online searches. 

In a move that sets up a major clash between Silicon Valley and Washington, American lawmakers said the tech giant could be forced into a huge shake-up.

Google's owner Alphabet could be ordered to sell parts of its business such as its Chrome internet browser and Android operating system. 

And, in a court filing published this week, the US Justice Department (DoJ) said it will seek to make sure Google cannot dominate the emerging artificial intelligence sector. 

But the tech giant, which is planning to appeal, said the proposals were 'radical' and could stifle American innovation. It comes after a judge in August found that Google has built an illegal monopoly in a landmark legal case. 

The Silicon Valley firm has become the go-to search engine for internet users, and accounts for around 90 per cent of online searches. 

The US government accused Alphabet of using its other products to get people to use its search engine, where it makes money by selling adverts.

Google may be forced to stop paying companies such as Apple billions of dollars for its search engine to be installed or set as the default on devices. 

And to prevent Google's dominance from extending into AI, the US may push Google to share its indexes, data and models with rivals. 

'It would be a huge change in how people and businesses use and interact with the internet in their lives, so this is clearly a high stakes game of poker,' said Ben Barringer, equity research analyst at Quilter. 

'For now, not a lot changes, and this will put a lid on investor enthusiasm for Alphabet for this year and most of next, until more is known. 

'This will be a long drawnout process with lots of negotiation still to take place. However, the DoJ has fired a shot across the bow of Alphabet.' 

Google said the proposals go far beyond the specific legal issues in this case'. 

Lee -Anne Mulholland, Google's vice-president of regulatory affairs, said: 'Government overreach in a fast-moving industry may have negative unintended consequences for American innovation and America's consumers. We look forward to making our arguments in court.' 

The firm, which has a valuation of more than $2trillion, said its search engine has won users with its quality, adding that it faces robust competition from rivals and other search engines are available.

Alphabet, the world's fourth-largest firm, is under mounting legal pressure from global competitors and regulators. 

In a separate case, a US judge ruled that Google must open up its app store Play to greater competition, including making Android apps available from rival sources. 

The company is fighting another case in the US that seeks the break-up of its web advertising business. And it faces similar competition challenges in the EU.