Members of the Sackler family, who own Purdue Pharma, the company that drove America’s opioid epidemic, appear for the first time to have acknowledged a role in the crisis by agreeing to pay tens of millions of dollars as part of a landmark legal settlement.

Purdue and some Sackler family members are to pay a total of $270m as part of an agreement to settle a lawsuit by the state of Oklahoma over the drug-maker’s aggressive and illegal marketing of the narcotic prescription painkiller OxyContin, made by Purdue, one of the drugs in a public health crisis that overall has claimed more than 350,000 lives over the past two decades.

The settlement does not reflect any admission of wrongdoing by the Sacklers.

Oklahoma’s attorney general, Mike Hunter, called the settlement a “monumental victory” and “a new day in battle against opioid epidemic”.

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The settlement is only a fraction of the billions of dollars the company made from pushing the mass prescribing of OxyContin, but is likely to set a benchmark for payments by Purdue in the hundreds of other lawsuits by states and cities across the US. Eight leading Sacklers who own Purdue were sued personally by more than 500 cities, counties and Native American tribes in a massive lawsuit in New York federal court last week.

Paul Hanly, a US lawyer heading a different federal lawsuit, which is consolidating about 1,600 legal actions by US cities and counties from states across the US against Purdue and other drug-makers and distributors in a court in Ohio, welcomed the payment. He especially noted the inclusion of members of the Sackler family in the settlement announced on Tuesday, who have been largely silent about the epidemic as it unfolded, intensified and persists, even as OxyContin sales made them billionaires. Sacklers will pay $75m toward the settlement announced.

“It’s the first time that we’ve seen any sort of public acknowledgement by the Sacklers concerning opioids,” Hanly said. The Sackler family was not a defendant in the Oklahoma claim.

In a statement later on Tuesday, the families of Mortimer and Raymond Sackler, the late brothers who owned Purdue Pharma at the height of the OxyContin crisis, said the contribution of $75m to the agreement with the Oklahoma attorney general’s office was voluntary and not an acknowledgement of wrongdoing. The money will go toward an addiction centre at Oklahoma State University.

Purdue Pharma issued a statement that did not acknowledge wrongdoing and characterised the financial settlement as intended to “help those who are battling addiction now and in the future”.

The trial in Oklahoma was highly anticipated despite being a smaller case than many underway, because it was going to be the first trial against Purdue to emerge from the growing pile of lawsuits by local and state governments against the company and, increasingly, leading family members.

Last week, the Tate group of art museums in the UK and the National Portrait Gallery in London, followed by the Solomon R Guggenheim Museum in New York, announced they would no longer take donations from Sackler family trusts, which have funded museums, universities and medical institutions in several countries.

Some institutions have faced protests by artists and activists, led by American art photographer Nan Goldin.

Hanly said the financial settlement with Oklahoma could lay the foundation for Purdue to settle for billions in the much larger lawsuits seeking compensation for alleged reckless and criminal mass prescribing of opioids. Thirty-six US states are suing Purdue and other companies separately through their own legal systems. And some of the major lawsuits directly sue named members of the Sackler family.

“It is a significant amount of money given the population of Oklahoma. We are hopeful that this signals the interest on the part of Purdue and other companies to consider resolution of all these thousands of claims,” he said.

Purdue was convicted of illegally marketing OxyContin in 2007, although members of the Sackler family were not charged. The current lawsuits allege that the company continued knowingly to make false claims about the safety and effectiveness of its drug, causing large numbers of people to become addicted.

The company has previously settled with West Virginia and Kentucky for a total of $34m without admitting liability.

Local and state governments in the US say they need money to fund the huge costs of treatment programmes for those who have become addicted, as well as looking after large numbers of children taken into care because their parents are dead or unfit due to addiction. The epidemic still claims around 150 lives a day.

Emily Walden, chair of the Fed Up Coalition of families hit by the epidemic and medical specialists, welcomed the settlement.

“We’re definitely headed in the right direction but they need to be paying a lot more. I hope the other companies also be held to paying hundreds of millions if not billions of dollars for what they’ve caused,” she said.

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Walden echoed a call by political leaders in some of the areas worst hit by the epidemic, for company executives responsible for the marketing strategies that pushed opioids to face prosecution.

Purdue reached the settlement two months before the first of a series of trials was to begin in Oklahoma. The case against 12 other drug manufacturers implicated in the epidemic will continue.

A woman who has been organizing hundreds of mothers to attend the Oklahoma trial said she’s “devastated” that a settlement has been reached with Purdue. Cheryl Juaire said on Tuesday that a full airing of the facts is the only way to fully hold the company accountable. Her 23-year-old son died of an overdose in 2011.

A key question is whether the financial settlement means the evidence against Purdue will be sealed. The company has been keen to avoid a hearing in open court, partly out of concern that it could open its executives to criminal prosecution.

The Associated Press contributed to this report.