US officials say Huawei maintains backdoors into telecom networks across the world, according to a report by The Wall Street Journal.

The news comes after years of escalating sanctions against the company — including an executive order in May that prohibited US companies from licensing tech to Huawei — but the justifications for those sanctions have remained vague and clouded by secrecy. Now, officials are getting specific, claiming the Chinese hardware manufacturer has maintained backdoors into some of the networks it builds, starting as early as 4G equipment sold in 2009. There’s also no hard evidence of the capability, but the claims are more specific than ever, and now coming from some of the nation’s top national security officials.

“We have evidence that Huawei has the capability secretly to access sensitive and personal information in systems it maintains and sells around the world,” national security adviser Robert O’Brien told the Journal.

There’s no indication of whether this capability has actually been used, although officials did tell the Journal that telecoms buying Huawei equipment are unaware of the company’s level of access.

Reached by The Verge, Huawei security chief Andy Purdy denied the allegations. “We vigorously deny the allegation that we retain any such capability,” Purdy said. “We also deny that we have ever improperly accessed customer information or customer data.”

The new US statements come after a surprise decision from the United Kingdom to allow Huawei to supply non-core equipment to the country’s networks. The US had lobbied heavily against Huawei’s inclusion in the run-up to 5G, but ultimately was unable to convince the country to entirely exclude the vendor.

It’s unclear how other countries will respond to the allegations, but Huawei says the new claims aren’t surprising, given the last year of escalating pressure.

“The US is committed to this, and I think it’s really prompted by the geopolitical situation between China and the US,” Purdy told The Verge. “The US is unwilling to consider the facts and the evidence, and they’re going to do whatever they can to block our ability to provide products to communication networks around the world.”

Update 2/11 5:15PM ET: Updated with comment from Huawei.