Less than 24 hours after President elect-Donald Trump fired off a pair of provocative tweets denouncing Beijing's trade policies and defending his precedent-shattering phone call with Taiwan's leader, China showed Washington it can play hardball, too: It changed its previous position and joined Russia to veto a U.S.-backed resolution calling for a seven-day humanitarian ceasefire in Aleppo, essentially condemning besieged Syrian civilians.

The Chinese action is just one of the myriad ways that Beijing can potentially upend American diplomatic priorities at the United Nations, from pushing to end the war in Syria, to punishing chemical weapons violators, to working to halt North Korea's nuclear weapons development.

Western diplomats fret that China's tough stance could be a harbinger of tougher times ahead. They anticipate China may well cast another veto, alongside Russia, to block a draft resolution currently under negotiation by the United States, Britain, and France that would sanction Syria for using chlorine bombs against at least three rebel-held towns.

The Chinese veto over Syria caught the United States and other U.N. Security Council members off guard. Though China had stood with Russia before, including four vetoes on Syrian U.N. resolutions since 2011, in recent months Chinese President Xi Jinping has put some distance between himself and Moscow as Russia's brutal air campaign in Aleppo drew international condemnation. On October 8, Russia was forced to cast the lone veto blocking a French- and Spanish-drafted resolution that would have demanded an end to the Russian and Syrian air strikes in Eastern Aleppo. China abstained.

In recent weeks, according to several council diplomats, all signs indicated China would abstain again on the new resolution, which was drafted by Egypt, New Zealand and Spain. It was seen as less controversial than the resolution China abstained on in October. Over the weekend, many even thought Russia itself might abstain, after Moscow secured a number of amendments, that would allow attacks against terrorists during the ceasefire and require moderate opposition forces to sever ties with terrorist groups like al Qaeda.

"The indications over the weekend were that [China] would abstain. The veto was a surprise," said a senior U.N.-based official.

As a veto-wielding U.N. power, China possesses enormous leverage to gum up the works at the United Nations, as it did in the 1990s, when it it cast vetoes to block U.N. peacekeepers from serving in U.N. operations in Guatemala and Macedonia because the countries established diplomatic relations with Taiwan.

In recent years, China has preferred to avoid such blunt displays of power, positioning itself instead as as responsible global power, committing troops for U.N. peacekeeping operations from Lebanon to South Sudan. Today, China has more peacekeepers deployed in overseas peace missions than any other great power. China is also angling for the top U.N. peacekeeping job, a post that would put them in charge of more than 100,000 blue helmets.

Samantha Power, the U.S. ambassador to the United Nations, recently praised Beijing for working closely with Washington to impose U.N. sanctions aimed at slashing North Korea's ability to export coal and earn money needed for its atomic ambitions.

It is hard to know for certain whether China's vote was designed more to punish Trump, or to reward Putin, or both. Moscow and Beijing have enjoyed closer diplomatic and economic ties in recent years, and both seek to nibble away at the U.S. role globally.

But the timing of the Chinese vote raised suspicions among some council diplomats that Trump's rapprochement with Taiwan prompted China to take a harder line. Trump roiled Chinese sensibilities Friday by taking a phone call from Taiwanese president Tsai Ing-wen - the first such call since the Nixon administration, and a sharp reversal to decades of following the so-called "One China" policy.

During the subsequent Syria debate, China's U.N. envoy, Liu Jieyi, struck an uncharacteristically tough tone with with his American and British counterparts after they questioned China's motives for the veto.

Michelle Sison, a senior U.S. official, accused China and Russia of cynically using their veto to demonstrate "that they do not want the suffering of eastern Aleppo to end."

Liu fired back, suggesting that U.S. military intervention in the region was at the root of the problem. "How did the situation in Syria come about, and how did the problems that other countries in the Middle East are dealing with reach the point where they are today?" he asked. "The historical record is very clear. Every member of the Council is very well aware of that. It cannot be changed by distorting the positions of some countries on the Council."

Matthew Rycroft, Britain's ambassador to the U.N., also jumped into the fray.

"Despite repeated pronouncements against politicization and in favor of dialogue, China has chosen to side with Russia - a party to the conflict," he told the council Monday. He said Beijing's veto came "because of their long-standing, misplaced faith in a despot who has killed nearly half a million of his own people, who has sanctioned the murder of civilians as they flee the bombed-out ruins of Aleppo - a despot who would rather reduce Syria to rubble than to negotiate an overdue peace."

The statement elicited a sharply worded response from Liu, who asked his British counterpart to cease "poisoning the atmosphere" in the Security Council.

"I would like to ask the representative of the United Kingdom what right he has to distort the position of other countries. . .Today is not the first time he has done that, and I hope that such abuse will not be repeated in the future."

