China is demanding the release of telecoms giant Huawei's chief financial officer, who has been detained in Canada.
Meng Wanzhou, the daughter of the company's founder, could face extradition to the US.
She was arrested in Vancouver on December 1, but the news was not made public at her request.
The charges remain unknown, but the US has been probing Huawei over possible violation of sanctions against Iran.
China says her detention is possibly a rights abuse.
Meng has sought a publication ban on the details of the arrest, which has been granted by the courts. Huawei said it was "not aware of any wrongdoing by Meng".
Huawei is one of the largest telecommunications equipment and services providers in the world, recently passing Apple to become the second-biggest smartphone maker after Samsung.
European shares hit a two-year low and indexes across Asia dropped sharply following the arrest.
A Chinese foreign ministry spokesperson told reporters: "The detention without giving any reason violates a person's human rights."
"We have made solemn representations to Canada and the US, demanding that both parties immediately clarify the reasons for the detention, and immediately release the detainee to protect the person's legal rights."
Beijing has itself frequently been accused by rights groups of rights abuses, including unexplained detentions.
Meanwhile, Meng's arrest comes at a sensitive time for US-China relations. The nations are engaged in a trade war that has seen both impose duties of billions of dollars on one another's goods.
But concerns the arrest would impact the 90-day tariff truce negotiated between the two nations at the G20 have not yet materialised. China announced in a regular press briefing on Thursday that it would "immediately" implement the measures agreed.
It also coincides with moves to restrict the use of Huawei technology in Western countries. The US, Australia and New Zealand have blocked the use of the Chinese firm's equipment in infrastructure for new faster 5G mobile networks.
Canada's ministry of justice confirmed the date and place of Meng's arrest and added: "She is sought for extradition by the United States, and a bail hearing has been set for Friday."
It said it could not say more as Meng had sought a ban on the publication of details and this had been ordered by the courts.
A spokesman for the US justice department in the Eastern District of New York - which Huawei said had brought the charges - declined to comment.