China’s Ministry of State Security says it is investigating a Chinese couple at a state agency on suspicion of spying for Britain. The development is the latest in a series of accusations exchanged between the two countries over alleged espionage.

The ministry disclosed on Monday that the couple are suspected of carrying out spying activities in China in cooperation with the British Secret Intelligence Service, MI6.

Its statement said that when the husband went to study in Britain in 2015, MI6 made contact, offering him substantial compensation to collect internal information from the Chinese government.

The ministry also said MI6 repeatedly asked for his wife’s cooperation, promising to double the reward.

It stressed that it has removed key operatives that Britain embedded in China.

The Chinese ministry previously announced in January that it found a foreign national working at a consulting firm spying in China in cooperation with MI6.

British authorities have also filed charges in separate cases against those they say were involved in Chinese espionage activities.

The two countries are increasingly at odds over Hong Kong and security issues.