China has charged an American woman with espionage after keeping her in custody since March last year, the country’s foreign ministry said Tuesday.

Houston businesswoman Sandy Phan-Gillis has been detained in the country by the Ministry of State Security — which oversees espionage and counterespionage — without proper cause, a move that has been criticized by the international community.

A United Nations working group on arbitrary detention said that the Chinese government informed it in April that Phan-Gillis was being accused of trying to steal state secrets and aiding an outside party in gathering national intelligence, the New York Times reported. She was formally arrested in October 2015, according to the group.

“Based on our understanding, Phan-Gillis, because of her suspected crimes of espionage, has been charged according to law by the relevant Chinese department,” Chinese Foreign Ministry spokeswoman Hua Chunying told a regular briefing, according to Reuters.

“China is a country ruled by law. The relevant Chinese department will handle the case strictly according to law,” she said, without elaborating.

The move could possibly escalate the already heightened tensions between China and the United States after a Chinese man — Su Bin, 51 — was jailed in the U.S. for 46 months after pleading guilty to conspiracy to hack sensitive military information by breaking into the computer networks of major U.S. defense contractors.

Tension over Chinese militarization in the South China Sea is another point of contention between the two nations. Reuters reported that in a letter transcribed by a U.S. consular official, Phan-Gillis said her detention was not because of any crime committed by her, but entirely political.

The charges have come days before U.S. President Barack Obama arrives in China on Saturday for a G-20 summit in the city of Hangzhou.