China and Serbia on Wednesday proclaimed an “ironclad friendship” and a “shared future” during a visit to Belgrade by the Chinese president, Xi Jinping, underlining the close political and economic ties between two countries that share a wariness of the United States.

Mr. Xi arrived in Serbia late Tuesday — the 25th anniversary of a mistaken 1999 airstrike involving the U.S. Air Force during the Kosovo war that destroyed the Chinese Embassy in Belgrade, the Serbian capital. Three Chinese journalists were killed in the strike.

Mr. Xi appeared briefly on Wednesday morning with the Serbian president, Aleksandar Vucic, before a cheering crowd of people, some of whom told Serbian media outlets they had been bused in by the ruling party, gathered in front of the Palace of Serbia, the former headquarters of the now defunct government of Yugoslavia that now houses Serbian government offices.

“The ironclad friendship between China and Serbia has withstood the test of international storms and tribulations,” Mr. Xi told Mr. Vucic in a meeting, according to an account from Xinhua, China’s official news agency. “It has a deep historical bedrock, a robust political foundation, wide-ranging common interests and a solid basis in public opinion.”

The leaders later signed an agreement declaring their intention to “deepen and elevate the comprehensive strategic partnership between China and Serbia,” and “build a new era of a community with a shared future,” local news outlets reported.

In contrast to his last visit to Eastern and Central Europe in 2016, during which he faced noisy protests in the Czech Republic, Mr. Xi h received a uniformly rapturous reception in Belgrade, with the authorities reportedly detaining potential protesters and mobilizing state workers to cheer him.

Sara Markovic, a Belgrade filmmaker, said in a telephone interview that her 63-year-old father, Dejan, a practitioner of China’s banned Falun Gong spiritual movement, and two fellow followers of what Beijing calls an “evil cult” had been taken into custody ahead of Mr. Xi’s visit.

A police arrest warrant said Ms. Markovic’s father was suspected of “endangering persons under international protection.”

Ms. Markov said her father had no plans to protest the Chinese leader’s visit and had been picked up because “our government wants to please the Chinese in every way possible” and was “acting like the CCP,” a reference to the Chinese Communist Party.

China routinely demands that foreign government’s hosting a visit by Mr. Xi remove protesters and even posters connected to Falun Gong or affiliated organizations like the Shen Yun dance troupe. Most European governments refuse, but Serbia has gone out of its way to show what Mr. Vucic on Wednesday described on Wednesday as “its reverence and love” for the Chinese leader.

China is Serbia’s largest foreign investor, and increasingly close economic relations have helped expand a relationship forged before the collapse of Yugoslavia, whose capital was Belgrade, in the early 1990s, through a shared wariness of Western and Soviet power.

The 25th anniversary of the NATO bombing has come at a time when Mr. Xi’s government is trying to steady relations with the United States and Western Europe. He had been expected to visit the bombed embassy site, which he visited on his last trip to Serbia in 2016 and is usually a mandatory stop for Chinese officials visiting Belgrade. But he had not appeared there before he leaving Belgrade Wednesday evening for his next stop, the Hungarian capital of Budapest, Europe’s only other reliably China-friendly capital.

His decision to skip the former embassy site, now a Chinese cultural center that features a black, tombstone-like marble tablet mourning Chinese and Serbian “martyrs,” suggested a desire to avoid rekindling anti-American passions that at the time of the bombing in 1999 led to angry protests by tens of thousands of Chinese around the U.S. embassy in Beijing, some throwing bottles and rocks.

“This we should never forget,” Mr. Xi said in a statement published on Tuesday by Politika, a Serbian newspaper, recalling that “25 years ago today, NATO flagrantly bombed the Chinese Embassy.” He said that China’s friendship with Serbia had been “forged with the blood of our compatriots” and “will stay in the shared memory of the Chinese and Serbian peoples.”

Beijing’s underlying suspicions about Western intentions, and the role of NATO, persist — a point that surfaced in Chinese official and media comments about the anniversary. But Mr. Xi refrained from the aggrieved outrage voiced in Beijing by the Chinese Foreign Ministry.

“The Chinese people will never forget this barbaric atrocity committed by NATO and will never accept such tragic history repeating itself,” Lin Jian, a spokesman for the ministry, told reporters in Beijing on Tuesday.

Serbia, which still harbors deep grievance over the defeat of Christian Serbs by Ottoman Turks in a battle in 1389, shares with China a view of itself as a righteous force wronged by hostile outsiders.

Serbia and China are also bound by mutual support for each other’s territorial claims — China’s to the breakaway island of Taiwan and Serbia’s to Kosovo, formerly Serbian land that declared an independent state after the NATO bombing campaign.

“Just as we have clear positions on the issue of Chinese integrity — that Taiwan is China — so they support the territory of Serbia without any reservation,” Mr. Vucic, who was Serbia’s information minister under President Slobodan Milosevic during the Kosovo war, said on Wednesday.

China, Mr. Xi said, “supports Serbia’s efforts to preserve its territorial integrity regarding Kosovo.”

Public opinion has soured dramatically on China in much of Europe, particularly in formerly Communist countries to the east, because of the war in Ukraine. But Serbia, which, like China, has close ties to Russia, has remained solidly pro-Chinese and still looks to China for billions of dollars in investment.

But as with nearly all European countries, Serbia has a widening trade deficit with China, a gap that Mr. Vucic hopes can be narrowed by a new free trade agreement that he said on Wednesday would allow Serbia to export 95 percent of its goods duty-free. While Serbia has few products that China needs, Mr. Vucic said Serbian farmers would benefit from new Chinese contracts for prunes, plums and blueberries.

Mr. Vucic was one of only two European leaders, along with Prime Minister Viktor Orban of Hungary, who attended a gathering in Beijing in October to celebrate Mr. Xi’s Belt and Road infrastructure program. President Vladimir V. Putin of Russia and dozens of other foreign leaders also attended.

Belgrade has been decked with Chinese flags and billboards paying tribute to “beloved Chinese friends.” Crowds lined the streets to welcome the Chinese leader, an outpouring of affection that opposition politicians said had been artificially manufactured by the authorities, which they said had ordered street cleaners and other state workers to skip work and cheer Mr. Xi.

Serbia’s state-owned television station even interrupted a broadcast of the Eurovision Song Contest, a hugely popular event watched by millions across Europe, to make way for coverage of a welcoming ceremony for Mr. Xi at Belgrade airport.

Chris Buckley contributed reporting from Taipei, Taiwan, and Alisa Dogramadzieva from Belgrade, Serbia.