The Chinese foreign ministry said it has detained two American citizens who run an English-teaching business in China, a development that comes as a trade war stokes broader tensions between the countries.

Jacob Harlan and Alyssa Petersen were detained in the eastern province of Jiangsu in late September “on suspicion of organizing others to cross the border,” foreign ministry spokesman Geng Shuang told reporters at a regular briefing in Beijing on Thursday. Family members of the pair have sought to raise money over the internet to fund their defence, with the post supporting Petersen calling the charge “bogus.”

Geng said that he “doesn’t see” how the detentions could be related to trade tensions between the world’s two largest economies. Chinese authorities alerted the U.S. consulate in Shanghai and arranged consular visits with U.S. diplomats for the two American citizens, Geng said.

The U.S. Embassy in Beijing said it was “aware of the detention of two U.S. citizens in China and the charges being brought against them by the provincial government.” “We take seriously our responsibility to assist U.S. citizens abroad and are monitoring the situation,” the embassy said.

Harlan in 2004 founded China Horizons, a business that helps bring teachers to China, and has been going back and forth between the U.S. and China since at least 2002, according to the company’s website.

Petersen is listed as an assistant director who has spent the last eight years “jumping in and out of China” as a volunteer and China Horizons employee.