Dozens of states and territories have launched the first US antitrust challenge to Google’s core search engine, the latest in a spate of lawsuits targeting the internet company.

The bipartisan group of 38 attorneys-general took aim at what it claimed were deliberate moves by the search giant to block rival services from reaching users.

The challenge to the way Google treats specialised, or “vertical”, search rivals follows a long-running campaign by companies such as Yelp, a local business search company and travel group Expedia. These sites have long argued that Google deliberately downplays them in its results in order to keep users tied to its own in-house services.

The suit includes claims that rivals were prevented from displaying their brands prominently in some forms of advertising and that they are excluded from the information boxes that often appear in prominent positions on Google results pages.

The claim echoes a case that the Federal Trade Commission sought to mount against Google eight years ago alleging broad “search bias”, but the US regulator ultimately backed down. Thursday’s case is more narrowly drawn.

Google immediately hit back at the attempt to prise open its search engine, claiming that such efforts would lead to a worse service for users.

“This lawsuit seeks to redesign search in ways that would deprive Americans of helpful information and hurt businesses’ ability to connect directly with customers,” said Adam Cohen, Google’s director of economic policy.

The company said directing users to the most useful results often meant bypassing what it called “aggregators” and “middlemen” such as Expedia and Yelp.

Yelp called the case “arguably more significant than previous lawsuits in that it strikes at the foundation of Google’s dominance: its search results”. By trying to open up Google’s search engine, it added, “we hope today’s action is the beginning of a return to a more vibrant and open internet”.

The latest case, led by Phil Weiser, the attorney-general of Colorado, came a day after 10 Republican-led states filed their own lawsuit claiming Google had used its control of the digital advertising supply chain to monopolise adverts and fix prices to suit itself.

Google also faces a complaint from the Department of Justice, backed by 12 states, over allegations that it created a web of contracts and partnerships to make it harder for rivals to reach an audience on smartphones or other devices.

Tom Miller, attorney-general of Iowa, said the number of cases reflected “a division of labour” among the states. The latest complaint “opens up another front in what Google has to deal with”, he said, adding: “In a world where they out-resource us, it’s another front.”

Beyond taking aim at Google’s search service, the latest case echoes actions that challenge the way Google guarantees distribution of its search engine via contracts with other companies. But it goes a step further in attacking deals that it said the company used to monopolise new markets such as smart speakers, televisions and cars.

These include limits Google allegedly places on hardware makers who use its voice assistant, preventing them from giving equal prominence to rival voice services under an arrangement known as “concurrency”.

In a parallel to the Texas-led case from Republican states lodged on Wednesday, the latest case also challenges Google’s advertising practices. It adds a new allegation that the company uses a tool called Search Ads 360 to make it harder for advertisers to compare prices on rival search engines and lock them into its own service.

The complaint, brought under section two of the Sherman Act, called for remedies that may include “structural divestitures”. However, Mr Weiser said it was too early to say whether the states would push for a break-up of Google if they win their case.