On Tuesday morning, U.S. Senator Mark Warner demanded to know whether Facebook had been sharing users’ personal data with Chinese phone companies that some perceive to be a national security risk, namely Huawei and ZTE. The social network has now responded in the affirmative, at least regarding Huawei, exacerbating the already-high tension between Facebook and U.S. lawmakers.

However, Facebook is insisting that the data in question never left people’s phones, and was not stored on Chinese servers. It also said it will wind down its deal with Huawei by the end of this week.