Chinese telecoms giant Huawei said on Thursday it has petitioned a US court to overturn a ban that prevents carriers in rural America from tapping an $8.5-billion federal fund to purchase the company’s equipment.

Huawei’s petition said the ban — imposed last month against the company and its Chinese rival ZTE on national security grounds — failed to substantiate claims that Huawei was a threat and was a violation of due process and thus “unlawful”.

“Huawei is a Chinese company. That is (Washington’s) only excuse,” Huawei’s chief legal officer Song Liuping told a press conference at company headquarters in the southern city of Shenzhen.

The petition to a US appeals court follows a lawsuit filed by Huawei in March that declared a 2019 US defence bill “unconstitutional” for barring government agencies from buying its equipment, services, or working with third parties that are Huawei customers.

The US campaign against Huawei is motivated by fears in Washington that the company is a potential security threat due to the background of its founder and CEO Ren Zhengfei, a former Chinese army engineer.

The concerns have escalated as Huawei has risen to become the world leader in telecom networking equipment and one of the top smartphone manufacturers, and following Beijing’s passage of a 2017 law that obliges Chinese companies to assist the government in matters of national security.

President Donald Trump moved in May to block American companies from doing business with Huawei, which US officials accuse of violating US sanctions on Iran.

But Trump has offered a series of temporary reprieves for Huawei to allow service providers covering remote rural areas time to comply with the ban.

Huawei has consistently dismissed the security accusations, saying Washington has provided no proof to back them up.