Uighurs and their supporters rally across the street from United Nations headquarters in New York on March 15. (Seth Wenig/AP)

The U.S. administration needs to press China harder over the detention of hundreds of thousands of Muslim Uighurs in “political education centers,” including dozens of relatives of reporters working for Radio Free Asia in Washington.

That’s the message conveyed in a letter from Sen. Marco Rubio (R-Fla.) and Rep. Christopher H. Smith (R-N.J.), the co-chairs of the Congressional-Executive Commission on China, to the U.S. ambassador in Beijing, Terry Branstad, on Wednesday.

Rubio and Smith cite credible media reports that between 500,000 and 1 million Uighurs have been sent to these centers for months of “political indoctrination” — calling it the largest mass incarceration of a minority population in the world today.

The Uighurs, a Muslim minority in western China, have faced decades of pressures from Beijing seeking to impose greater central authority over the region and suppress a low-level Uighur separatist movement.

The call for a tougher political stance by Washington comes as the Trump administration and China are locked in a deepening dispute over tariffs and trade.

Many Uighurs have been reportedly detained for praying, wearing “Islamic” clothing or having foreign connections, such as having previously traveled abroad or having relatives in another country.

Among those rounded up are dozens of family members of six journalists from the Washington-based Radio Free Asia, who have reported on the deepening crackdown in China’s western region of Xinjiang, officially known as the Xinjiang Uighur Autonomous Region (XUAR).

Four of the reporters are naturalized U.S. citizens, and two have reason to believe their family members were detained directly because of their reporting. 

“These detentions serve to intimidate the families of U.S. government employees and undermine some of the most effective reporting from the XUAR, a region which is increasingly off limits to international reporters, members of civil society and diplomats,” Rubio and Smith wrote.

They cited reports of deaths and torture in the detention centers. They also raised alarms over a digital surveillance system in the region so pervasive that every aspect of daily life is monitored, through facial recognition cameras, mobile phone scans, DNA collection and an extensive and intrusive police presence.

Rubio and Smith asked Branstad to personally lead efforts for the release of the relatives of the Radio Free Asia reporters. 

“If there is no immediate resolution of these cases, we ask that the State Department consider denying visas to executives or administrative staff of Chinese-run state media operating in the United States,” they wrote.

They requested the Embassy to compile a list of Xinjiang officials responsible for the arbitrary detentions and abuse, for possible sanction under the Global Magnitsky Act.

The embassy, in a emailed statement on Thursday, said it was “concerned” by the reports of the detentions of the reporters’ relatives, and was “deeply troubled” by reports of the deepening crackdown on Uighurs and other Muslims in China. Branstad has raised these concerns with the Chinese government, the embassy said. 

“We call on China to release all prisoners of conscience, and to respect the human rights and fundamental freedoms of all its citizens,” it said.