BEIJING — The US 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 Senator Marco Rubio, a Florida Republican, and Representative Chris Smith, a New Jersey Republican, the cochairmen of the Congressional-Executive Commission on China, to the US ambassador in Beijing, Terry Brandstad, 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.’’

The Uighurs, a Muslim minority in western China, have faced decades of pressures from Beijing seeking to impose greater central authority over the region. 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.

Among those rounded up were 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 Uyghur Autonomous Region (XUAR).

Four of the reporters are naturalized US 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 US 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.

WASHINGTON POST