The Chinese government rarely passes up a chance to accuse the United States of military adventurism and hegemony. In the case of Afghanistan, though, it has changed its tone, warning that Washington now bears the responsibility for the hasty end to its two-decade war there.

“The United States, which created the Afghan issue in the first place, should act responsibly to ensure a smooth transition in Afghanistan,” China’s foreign minister, Wang Yi, said this month at a forum in Beijing. “It should not simply shift the burden onto others and withdraw from the country with the mess left behind unattended.”

While China has not called on President Biden to reverse the military withdrawal he ordered, statements by senior officials made it clear that they would blame the United States for any insecurity that spreads in the region.

China’s leader, Xi Jinping, and President Vladimir V. Putin of Russia — neither of them close friends of the American president — raised concerns about the withdrawal in a call the two leaders had in late June, citing “the increasingly complicated and severe security situation,” according to the state news agency Xinhua.

An explosion and vehicle crash that killed nine Chinese workers in Pakistan on Wednesday has punctuated China’s fears of regional instability in the wake of the final American military withdrawal from Afghanistan and the chaos that is now spreading across the country.

China was quick to describe the explosion as an act of terrorism. Pakistan later described it as an accident, but the details remain murky, and China has previously found itself the target of threats from those opposed to its growing economic and diplomatic influence in the region.

Pakistan’s information minister, Fawad Chaudhry, said on Thursday that investigators had found traces of explosives, presumably on the bus carrying the Chinese workers. “Terrorism cannot be ruled out,” he wrote on Twitter.

“They’re certainly feeling nervous,” said Barnett R. Rubin, a former State Department official and United Nations adviser on Afghanistan who is a senior fellow at New York University’s Center on International Cooperation.

With only a residual military contingent left to protect the American Embassy in Kabul, the Taliban have been steadily expanding their political control as Afghan government forces crumble or retreat. This month, Taliban forces seized Badakhshan, the province that reaches the mountainous Chinese border through the Wakhan Corridor.

While that narrow territory poses little direct security threat, China fears that the breakdown of order in Afghanistan could spill out of the country to other neighbors, including Tajikistan, Kazakhstan and Pakistan.

Mr. Wang is traveling through Central Asia this week with the Afghan situation high on the agenda.

“We don’t want to see a turbulent country around us that becomes such a soil for terrorist activities,” said Li Wei, an analyst at the China Institutes of Contemporary International Relations, a research organization in Beijing affiliated with the Ministry of State Security.

The Taliban, when they governed Afghanistan before the Sept. 11, 2001, attacks, gave haven to some Uyghur fighters resisting Chinese rule in Xinjiang, the predominantly Muslim province in western China that the fighters call East Turkestan.

Twenty-two of those fighters ended up in American custody in the prison at Guantánamo Bay, Cuba, only to be released slowly to several other countries, including Albania, Slovakia, Bermuda and Palau. Uyghur militants have also fought in Syria’s civil war, and there are reports that some have returned to Afghanistan.

“If there’s more disorder in Afghanistan, the Uyghurs could get a foothold again, or a bigger one,” Mr. Rubin said.

After the Sept. 11 attacks, the United States designated the East Turkestan Islamic Movement as a terrorist organization, in part to cultivate China’s support for American efforts in the “war on terror.” The Trump administration revoked the designation last year, saying that there was no evidence that the group continued to carry out attacks. China has cited the threat of Uyghur extremism as a reason for its mass detention camps in Xinjiang.

According to the United Nations, the Uyghur group once maintained links to Al Qaeda and organized attacks on targets inside and outside of China, including ones in Xinjiang that killed 140 people in 1998.

Liu Yunfeng, the director of the Counter-Terrorism Bureau of the Ministry of Public Security, said this week at a news conference that while there had been no major terrorist attack in China in the past four years, the East Turkestan Islamic Movement continued to promote terrorism from abroad and train fighters “to sneak into our territory.”

“We still need to maintain a high degree of vigilance,” he said, according to a transcript posted by the ministry.

With the American withdrawal on the horizon, China has sought to keep channels open to both the Taliban and Afghan forces, appealing for a peaceful resolution to decades of conflict that predated the American intervention. It has been a delicate diplomatic balance.

China has praised the current Afghan government, including what it says are efforts to fight the East Turkestan militants. It also played host to a delegation of Taliban leaders in 2019. While China has said little about the nature of its discussions with the group, it has muted its criticism as the American-led military presence winds down.

In recent statements, Taliban representatives have also sought to assuage China’s concerns about its past support for enemies of Chinese rule, saying a restored Taliban government would pose no threat to the country. In fact, it would welcome Chinese investments.

As the Taliban have steadily gained ground, China has left its diplomatic options open. The Global Times, a Communist Party newspaper that generally reflects the government’s hawkish side, suggested this week that fears about the collapse of the current Afghan government were overstated.

“With the evolving Afghanistan situation, the Taliban is quietly transforming itself to improve its international image, easing the concerns of and befriending neighboring countries,” the newspaper wrote on Tuesday.

Such views also reflect China’s close relationship with Pakistan, which provided support for the Taliban leadership during the long American involvement in Afghanistan.

After Chinese officials initially denounced Wednesday’s deaths in Pakistan as a terrorist attack, they tempered their remarks when the Pakistani Foreign Ministry released a statement saying that the explosion that sent a truck tumbling into a ravine was caused by a mechanical malfunction.

Exactly what happened remains unclear, however. At least two Pakistani paramilitary soldiers and two other civilians died, while more than 40 people were injured. It was not clear if the soldiers were guarding the workers as they traveled to a Chinese-built hydroelectric project at Dasu, a city in the country’s rural northwest, about 100 miles from the capital, Islamabad.

China has faced terrorist threats in Pakistan before. In 2018, three suicide attackers stormed the Chinese Consulate in Karachi, killing two police officers and two civilians before being killed themselves. The group that claimed responsibility for that attack, the Baluchistan Liberation Army, attacked a luxury hotel in Gwadar a year later, saying they were targeting Chinese guests.

In April, a different group attacked a hotel in Quetta, the provincial capital of Baluchistan, only moments before China’s ambassador was scheduled to arrive. Although it was not clear if the attackers knew of the ambassador’s arrival, the group that claimed responsibility, the Pakistani Taliban, or Tehrik-i-Taliban Pakistan, said its intended targets were “locals and foreigners” staying at the hotel.

After speaking with Pakistan’s foreign minister about the explosion on Wednesday, Mr. Wang, the foreign minister, called for greater security measures for Chinese construction projects in Pakistan, many of them being built under China’s “belt and road” initiative.

Chinese officials have offered to extend those projects to Afghanistan, but have made little progress. Previous Chinese projects there failed to live up to expectations, most prominently a copper mine concession that Chinese companies acquired in 2007.

“If it is a terrorist attack,” Mr. Wang said of the episode on Wednesday, “the perpetrators must be arrested immediately, and the perpetrators must be severely punished.”