WASHINGTON — Over three months, senior Biden administration officials held half a dozen urgent meetings with top Chinese officials in which the Americans presented intelligence showing Russia’s troop buildup around Ukraine and beseeched the Chinese to tell Russia not to invade, according to U.S. officials.

Each time, the Chinese officials, including the foreign minister and the ambassador to the United States, rebuffed the Americans, saying they did not think an invasion was in the works. After one diplomatic exchange in December, U.S. officials got intelligence showing Beijing had shared the information with Moscow, telling the Russians that the United States was trying to sow discord — and that China would not try to impede Russian plans and actions, the officials said.

The previously unreported talks between American and Chinese officials show how the Biden administration tried to use intelligence findings and diplomacy to persuade a superpower it views as a growing adversary to stop the invasion of Ukraine, and how that nation, led by President Xi Jinping, persistently sided with Russia even as the evidence of Moscow’s plans for a military offensive grew over the winter.

This account is based on interviews with senior administration officials with knowledge of the conversations who spoke on the condition of anonymity because of the sensitive nature of the diplomacy. The Chinese Embassy did not return requests for comment.

China is Russia’s most powerful partner, and the two nations have been strengthening their bond for many years across diplomatic, economic and military realms. Mr. Xi and President Vladimir V. Putin of Russia, two autocrats with some shared ideas about global power, had met 37 times as national leaders before this year. If any world leader could make Mr. Putin think twice about invading Ukraine, it was Mr. Xi, went the thinking of some U.S. officials.

But the diplomatic efforts failed, and Mr. Putin began a full-scale invasion of Ukraine on Thursday morning after recognizing two Russia-backed insurgent enclaves in the country’s east as independent states.

Some American officials say the ties between China and Russia appear stronger than at any time since the Cold War. The two now present themselves as an ideological front against the United States and its European and Asian allies, even as Mr. Putin carries out the invasion of Ukraine, whose sovereignty China has recognized for decades.

The growing alarm among American and European officials at the alignment between China and Russia has reached a new peak with the Ukraine crisis, exactly 50 years to the week after President Richard M. Nixon made a historic trip to China to restart diplomatic relations to make common cause in counterbalancing the Soviet Union. For 40 years after that, the relationship between the United States and China grew stronger, especially as lucrative trade ties developed, but then frayed due to mutual suspicions, intensifying strategic competition and antithetical ideas about power and governance.

In the recent private talks on Ukraine, American officials heard language from their Chinese counterparts that was consistent with harder lines the Chinese had been voicing in public, which showed that a more hostile attitude had become entrenched, according to the American accounts.

On Wednesday, after Mr. Putin ordered troops into eastern Ukraine but before its full invasion, Hua Chunying, a Foreign Ministry spokeswoman, said at a news conference in Beijing that the United States was “the culprit of current tensions surrounding Ukraine.”

“On the Ukraine issue, lately the U.S. has been sending weapons to Ukraine, heightening tensions, creating panic and even hyping up the possibility of warfare,” she said. “If someone keeps pouring oil on the flame while accusing others of not doing their best to put out the fire, such kind of behavior is clearly irresponsible and immoral.”

She added: “When the U.S. drove five waves of NATO expansion eastward all the way to Russia’s doorstep and deployed advanced offensive strategic weapons in breach of its assurances to Russia, did it ever think about the consequences of pushing a big country to the wall?” She has refused to call Russia’s assault an “invasion” when pressed by foreign journalists.

Ms. Hua’s fiery anti-American remarks as Russia was moving to attack its neighbor stunned some current and former U.S. officials and China analysts in the United States. But the verbal grenades echo major points in the 5,000-word joint statement that China and Russia issued on Feb. 4 when Mr. Xi and Mr. Putin met at the opening ceremony of the Winter Olympic Games in Beijing. In that document, the two countries declared their partnership had “no limits” and that they intended to stand together against American-led democratic nations. China also explicitly sided with Russia in the text to denounce enlargement of the North Atlantic Treaty Organization.

Last Saturday, Wang Yi, the Chinese foreign minister, criticized NATO in a video talk at the Munich Security Conference. European leaders in turn accused China of working with Russia to overturn what they and the Americans say is a “rules-based international order.” Mr. Wang did say that Ukraine’s sovereignty should be “respected and safeguarded” — a reference to a foreign policy principle that Beijing often cites — but no Chinese officials have mentioned Ukraine in those terms since Russia’s full invasion began.

“They claim neutrality, they claim they stand on principle, but everything they say about the causes is anti-U.S., blaming NATO and adopting the Russian line,” said Evan Medeiros, a Georgetown University professor who was senior Asia director at the White House National Security Council in the Obama administration. “The question is: How sustainable is that as a posture? How much damage does it do to their ties with the U.S. and their ties with Europe?”

The Biden administration’s diplomatic outreach to China to try to avert war began after President Biden and Mr. Xi held a video summit on Nov. 15. In the talk, the two leaders acknowledged challenges in the relationship between their nations, which is at its lowest point in decades, but agreed to try to cooperate on issues of common interest, including health security, climate change and nuclear weapons proliferation, White House officials said at the time.

After the meeting, American officials decided that the Russian troop buildup around Ukraine presented the most immediate problem that China and the United States could try to defuse together. Some officials thought the outcome of the video summit indicated there was potential for an improvement in U.S.-China relations. Others were more skeptical, but thought it was important to leave no stone unturned in efforts to prevent Russia from attacking, one official said.

Days later, White House officials met with the ambassador, Qin Gang, at the Chinese Embassy. They told the ambassador what U.S. intelligence agencies had detected: a gradual encirclement of Ukraine by Russian forces, including armored units. William J. Burns, the C.I.A. director, had flown to Moscow on Nov. 2 to confront the Russians with the same information, and on Nov. 17, American intelligence officials shared their findings with NATO.

At the Chinese Embassy, Russia’s aggression was the first topic in a discussion that ran more than one and a half hours. In addition to laying out the intelligence, the White House officials told the ambassador that the United States would impose tough sanctions on Russian companies, officials and businesspeople in the event of an invasion, going far beyond those announced by the Obama administration after Russia seized Ukraine’s Crimean Peninsula in 2014.

The U.S. officials said the sanctions would also hurt China over time because of its commercial ties.

They also pointed out they knew how China had helped Russia evade some of the 2014 sanctions, and warned Beijing against any such future aid. And they argued that because China was widely seen as a partner of Russia, its global image could suffer if Mr. Putin invaded.

The message was clear: It would be in China’s interests to persuade Mr. Putin to stand down. But their entreaties went nowhere. Mr. Qin was skeptical and suspicious, an American official said.

American officials spoke with the ambassador about Russia at least three more times, both in the embassy and on the phone. Wendy R. Sherman, the deputy secretary of state, had a call with him. Mr. Qin continued to express skepticism and said Russia had legitimate security concerns in Europe.

The Americans also went higher on the diplomatic ladder: Secretary of State Antony J. Blinken spoke to Mr. Wang about the problem in late January and again on Monday, the same day Mr. Putin ordered the new troops into Russia-backed enclaves of Ukraine.

“The secretary underscored the need to preserve Ukraine’s sovereignty and territorial integrity,” said a State Department summary of the call that used the phrase that Chinese diplomats like to employ in signaling to other nations not to get involved in matters involving Taiwan, Tibet, Xinjiang and Hong Kong, all considered separatist problems by Beijing.

American officials met with Mr. Qin in Washington again on Wednesday and heard the same rebuttals. Hours later, Mr. Putin declared war on Ukraine on television, and his military began pummeling the country with ballistic missiles as tanks rolled across the border.