STOCKHOLM (Reuters) - The U.S. Environmental Protection Agency said on Wednesday it has been in talks with Volvo over the last few weeks about an issue with catalytic converters causing some of its vehicles to exceed nitrogen oxide emission limits.

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Volvo warned a day earlier that some of its truck and bus engines could be exceeding limits for nitrogen oxide emissions due to an emissions control component it uses degrading more quickly than expected.

The Swedish truckmaker said it could face material costs to deal with the issue largely affecting trucks and buses sold in North America and Europe, its two largest markets, and that it was working with authorities to find a solution.

The EPA, in an emailed statement, told Reuters on Wednesday that the agency was aware of the situation, which it said involved Volvo heavy duty trucks.

“Over the last few weeks, EPA and the California Air Resources Board (CARB) have been communicating with Volvo about the problem and are now continuing to meet with the company to develop plans to quickly address this situation,” the EPA statement said.

A U.S. government official briefed on the matter said on Wednesday that regulators do not believe excess emissions are the result of a "defeat device" or intentional misconduct as in the case of Volkswagen AG's VOWG_p.DE excess diesel emissions, but rather is believed to be the result of a faulty component and a recall is expected.

Asked why Volvo had waited a couple of weeks before informing the market, a Volvo spokesman said the company needed to determine whether this would be a large issue and it was standard protocol to inform authorities first.

“Authorities and legal bodies are normally informed prior to the markets because we inform them even if the problem is very, very small,” he said.

Volvo did not say when the affected trucks were sold or how many are impacted. It said that all products equipped with the component met emissions limits at delivery.

The company sold 51,693 trucks in North America last year and another 115,863 in Europe.

EPA and CARB declined to comment about how many trucks were involved, while a spokesman for Volvo said it was too early to know.

“We... are working with the company to more fully understand what’s going on,” a spokesman for CARB said in a brief separate comment, without giving more details.