Deputy Secretary of State Kurt Campbell, a key architect of a 15-year push for the United States to reorient its foreign policy toward Asia, also urged greater US investment in advanced technology to compete better with China.

"There is a recognition that this is the most significant challenge in our history," Campbell told the House Foreign Affairs Committee.

"Frankly, the Cold War pales in comparison to the multifaceted challenges that China presents," he said.

"It's not just a military challenge; it's across the board. It is in the Global South. It is in technology. We need to step up our game across the board."

Asked about the remarks on Thursday, a spokesman for China's foreign ministry said they "disregard facts, openly and wantonly exaggerate the China threat, and clamour for camp confrontations".

Regarding China as the United States' greatest challenge was a mistake, Lin Jian said at a regular press conference.

"China urges the United States to abandon Cold War zero-sum thinking, stop spreading the China threat theory, and stop distorting China's strategic intentions," he added.

Campbell's tough talk comes despite a thaw in relations between the United States and China under President Joe Biden.

Republican presidential candidate Donald Trump speaks more frequently in Cold War terms about confronting Beijing.

- 'Need more support' -

Biden and his political heir Kamala Harris have supported dialogue with China even as their administration presses ahead with tough measures including a sweeping ban on exports of advanced chips.

Biden's administration has also been pressing China about technology exports to Russia that US officials say have allowed Moscow to ramp up military production for its war in Ukraine.

"The challenge is, we've got to get more support here on this," Campbell said of US sanctions on Chinese firms, an issue he said he has been raising on visits to Europe.

Campbell said that most of Washington's European allies shared concerns about China's ties with Moscow but were still reeling from the "huge shock" of slashing energy imports from Russia since its invasion of Ukraine.

"For many of these countries, doing business with China has been a big deal for 15 or 20 years," he said.

Acting on China, after Russia, could feel like "kind of a one-two punch. You can understand leaders in Europe have some anxieties."

China argues that, unlike the United States, it is not providing weapons to either Russia or Ukraine, but Washington says Beijing is providing support that has military uses.

- Pushing for prisoners -

Campbell contended that the Biden administration has strengthened the US position since taking over from Trump, in part by bolstering alliances.

"Four years ago, the general view globally was that China had eaten our lunch... I do not think that is what the general belief is today," he said.

Since a summit last year between Biden and President Xi Jinping in California, China has agreed to key US requests of restoring military communications and cracking down on ingredients in fentanyl, the drug behind a US overdose epidemic.

Meeting another key ask of the Biden administration, China freed an American pastor, David Lin, who had been detained since 2006, the State Department confirmed Sunday.

The United States had raised the case of Lin and other detained Americans with China, including when Secretary of State Antony Blinken met his counterpart Wang Yi on the sidelines of a meeting in Laos in July.

The State Department considers two other US citizens, Kai Li and Mark Swidan, to be wrongfully detained by China, but activists say far more Americans are behind bars or prohibited from exiting.

The mother of Swidan, detained over drug trafficking charges he denies, told a separate congressional hearing that Biden needs to engage with China on its proposals to free him.

"His case is a clear injustice, yet it continues to be ignored by those with the power to act," she said in a statement to the Congressional-Executive Commission on China.

Peter Humphrey, who was detained with his wife in China from 2013 to 2015 and has since become a specialist on such cases, said a "massive number" of Americans cannot publicly raise their cases for fear of retribution by Beijing.

He said he was held with 11 other men in a packed cell with no privacy or furniture, sleeping on the floor and eating from dog bowls pushed under the bars.

He said he lost 22 pounds (10 kilos) while in detention, which he described as "torture designed to crush the human spirit and force out a confession."