The White House appeared to mute its criticism of China's Communist Party in recent weeks in order to push forward trade negotiations with Beijing.

However, progress has stalled despite President Donald Trump and Chinese President Xi Jinping promising last month to resume talks.

On Thursday, Secretary of State Mike Pompeo and Vice President Mike Pence renewed their criticism of China's crackdown on its Uighur Muslim minority.

Pompeo called the Uighur oppression "truly the stain of the century."

Trump also made his first public remarks on the crisis this week but appeared to have little knowledge of the details of the crisis.

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President Donald Trump's administration is renewing its attacks on China's human-rights crisis as trade negotiations between Washington and Beijing appear to have stalled.

Secretary of State Mike Pompeo on Thursday singled out China's oppression of the Uighurs, a mostly-Muslim ethnic minority living in the country's west.

The Uighurs are subject to severe human-rights abuses, with China installing a hi-tech surveillance state in their home region of Xinjiang because it sees the entire ethnic group as a national-security threat.

Read more: Jailing Muslims, burning Bibles, and forcing monks to wave the national flag: How Xi Jinping is attacking religion in China

Men install a surveillance camera in a shopping street in the Old Town of Kashgar, Xinjiang, in March 2017. REUTERS/Thomas Peter

Pompeo told a conference on religious freedom in Washington, DC: "China is home to one of the worst human rights crises of our time; it is truly the stain of the century."

He added that China tried to forbid other countries from sending delegations to the US-led conference, saying: "If you are here today, and you're a country which has defied the Chinese pressure to come here, we salute you and we thank you. If you have declined to attend for the same reason, we took note."

Vice President Mike Pence told the same conference: "Whatever comes of our negotiations with Beijing, you can be assured that the American people will stand in solidarity with people of all faith in the People's Republic of China," referring to the US's trade talks with China.

"We will pray for the day that they can live out their faith freely without fear of persecution," he said.

US Secretary of State Mike Pompeo addresses the second Ministerial to Advance Religious Freedom at the State Department in Washington, DC, on July 18, 2019. Mary F. Calvert/Reuters

While Pompeo and Pence have criticized China's human-rights record in the past, both men have kept silent over for the past few weeks, likely in exchange for progress in the protracted US-China trade war.

Last month Pence called off a speech poised to fiercely criticize China's Uighur crisis a week before President Donald Trump was due to meet his Chinese counterpart, Xi Jinping, at the G20 summit on June 29.

Trump also promised Xi in that meeting that the US would mute its support for the anti-China protests in Hong Kong in exchange for re-opening trade talks, the Financial Times reported earlier this month.

The US and Chinese delegations, led by Trump and Xi, at the G20 summit in Osaka on June 29, 2019. Reuters

However, trade negotiations appear to have stalled.

There have no face-to-face trade talks since Trump and Xi's G20 meeting, The Wall Street Journal reported Wednesday, despite promises on both sides to restart talks. Bloomberg reported that senior officials have spoken by phone twice, however.

Trump said shortly after the G20 that he would allow some US firms to start selling products to Huawei, the Chinese telcom giant whom Washington has labeled a national-security threat.

But US officials still haven't decided what products they would allow to be sold to Huawei without jeopardizing national security or giving the company an advantage in the global tech war, the Journal said.

Trump on Wednesday also renewed threats that he would start placing tariffs on another $325 billion worth of Chinese goods.

Trump speaks to reporters in the Oval Office while hosting victims of religious persecution around the world on July 17, 2019. Jewher Ilham, a Uighur whose father is detained in China, is not in frame. Leah Millis/Reuters

The president made his first public remarks on the Uighur crisis on Wednesday — calling it "tough stuff" — but appeared not to know details of the persecution.

In a meeting with victims of religious persecution from around the world, he appeared not to know about internment camps in Xinjiang, or where Xinjiang was at all.

Below is a transcript of his conversation, provided by the White House, with Jewher Ilham, whose father was taken in 2013 and later sentenced to life in prison for allegedly inciting "separatism."

Ilham: Mr President, one to three million Uighur population are locked up in concentration camps in China, including my father, who is now serving a life sentence. I haven't seen him since 2013.



Trump: Where is that? Where is that in China?



Ilham: That's in [the] west part of China. The region — in Chinese, it's called "Xinjiang." We call it "Uighur region." So far, we had —



Trump: How long? How long has your father been gone?



Ilham: He has been in jail for five years, and we don't know how long he will still be in there.



Trump: Do you have any communication with him?



Ilham I haven't heard about him since 2017, because that's when the concentration camps started. Anyone who goes to ask about anybody's family members' news will never make their way back to their own homes.



Trump: That's tough stuff.

A masked Uighur boy takes part in a protest against China in Istanbul, Turkey, in November 2018. Murad Sezer/Reuters

Beijing has detained up to 1.5 million Uighurs in prison-like camps, where people are reportedly physically and psychologically tortured.

Uighurs are frequently detained and arrested for minor infractions including keeping in touch with family outside the region.