China accused the US of infiltrating Huawei Technologies Co. servers beginning in 2009, part of a broad-based effort to steal data that culminated in tens of thousands of cyber-attacks against Chinese targets last year.

The Tailored Access Operations unit of the National Security Agency carried out the attacks in 2009, which then continuously monitored the servers, China’s Ministry of State Security said in a post on its official WeChat account on Wednesday. It didn’t provide details of attacks since 2009.

Cyberattacks are a point of tension between Washington and Beijing, which has accused its political rival of orchestrating attacks against Chinese targets ever since Edward Snowden made explosive allegations about US spying. Washington and cybersecurity researchers have said the Asian country has sponsored attacks against the West.

The ministry’s accusations emerged as the two countries battle for technological supremacy. Huawei in particular has spurred alarm in Washington since the telecom leader unveiled a smartphone powered by an advanced chip it designed, which was made by Semiconductor Manufacturing International Corp. That’s in spite of years-long US sanctions intended to cut Huawei off from the American technology it needs to design sophisticated chips and phones.

Read more: US Probes Made-in-China Chip as Tensions Flare Over Technology

The US has been “over-stretching” the concept of national security with its clampdown on Chinese enterprises, Foreign Ministry spokeswoman Mao Ning told reporters at a regular press briefing in Beijing on Wednesday.

“What we want to tell the US is that suppression and containing of China will not stop China’s development. It will only make us more resolved in our development,” Mao said.

On Tuesday, US Commerce Secretary Gina Raimondo said she was “upset” when Huawei released the Mate 60 Pro during her visit to China last month, but noted the US has no evidence the Asian nation can make the advanced semiconductors powering the handset “at scale.”