SEOUL—China is engaged in an international influence campaign to block South Korea from joining U.S.-led regional missile defenses, according to current and former U.S. officials.

President Xi Jinping of China, as part of the operation, directly appealed to President Park Geun-hye of South Korea not to allow U.S. military forces to go ahead with plans to deploy the Army’s Terminal High-Altitude Area Defense, or THAAD, a highly effective anti-missile system capable of knocking out both North Korean and some Chinese missiles, said the officials.

As leverage, the hardline Chinese leader is offering Seoul increased trade and business if THAAD deployment is scuttled.

Additionally, Beijing is pressuring the Park administration to allow China’s controversial Huawei Technologies to bid on telecommunications infrastructure projects in South Korea.

Huawei has been linked by the U.S. government to espionage plots conducted through its network equipment. The company has been blocked several times from merging with U.S. companies over the cybersecurity concerns. Xi wants Huawei to be allowed to bid on major contracts in South Korea.

The U.S. military is concerned that allowing Huawei into communications networks will increase the vulnerability of the country to cyberattacks in a crisis or conflict. China remains a major political and economic backer of North Korea.

The controversy over missile defense has the potential to upset the U.S.-South Korea alliance, one of America’s closest relationships in Asia.

The anti-missile defense campaign here is a key part of a Beijing’s regional strategy of undermining U.S. influence and ultimately seeking to drive U.S. military forces out of the region.

China wants to use South Korea to weaken and erode U.S.-Japan-South Korea collective defenses, the cornerstone of peace and stability in East Asia since the 1950s, in a bid for Beijing to gradually replace the United States as the most significant Asia-Pacific power, said a U.S. official who specializes in China affairs.

"That's Beijing’s strategic objective," the official said, adding that the strategy includes stoking anti-Japan sentiment with propaganda about Tokyo’s colonial and wartime past. The Chinese want to prevent South Korea from focusing on more imminent and dangerous threats posed by China and North Korea, the official said.

"Unfortunately, the South Korean leadership seems to have easily fallen for Beijing’s calculations," the official said.

THAAD defenses were requested by Gen. Curtis Scaparrotti, commander of U.S. forces in Korea, last year to counter what he said were "evolved" North Korean missile threats. Site surveys of basing locations for THAAD batteries were conducted last year.

The U.S. military currently has deployed Patriot PAC-3 missiles defenses in the country to protect military facilities. South Korea last year asked to buy 136 PAC-3s and related equipment.

Patriot missile defenses are effective against short-range missiles but lack capabilities needed to counter North Korea’s growing arsenal of intermediate and long-range missiles.

Those weapons include the Musudan intermediate-range missile, the KN-08 road-mobile lCBM, and the developmental KN-11 submarine-launched ballistic missile. The KN-11 was flight tested for the first time last month, according to U.S. officials.

China’s campaign to block THAAD deployments are based on fears the defense radar and interceptors could be used against some of the thousands of Chinese missiles that form the backbone of China’s military strike capabilities, officials said.

The missiles include four types of road-mobile, medium, and long-range missiles. China’s aircraft-carrier killing DF-21D anti-ship ballistic missile and submarine-launched JL-2 missiles are among the weapons the Chinese believe could be countered by THAAD.

Additionally, the deployment of the high-powered THAAD radar can provide coverage over an area of some 600 miles, providing detection of missile launches inside China.

Obama administration officials have done little to counter the Chinese propaganda campaign.

Deputy Secretary of State Tony Blinken said during a visit here last month that THAAD would be aimed at North Korea. He also sought to downplay the deployment plans and said any decision on fielding the weapon would be made with the South Korean government.

THAAD units are equipped with a high-technology radar capable known as the AN/TPY-2. The X-band radar can spot, track, and identify ballistic missile launches over long distances and very high altitudes.

The radar also could be used for "cooperative engagement" missile defense—networked sensors and communications that allows rapid sharing and exchange of launch and targeting data.

Since the 1990s, China’s People’s Liberation Army has invested heavily in building missile forces. As a result China is trying to prevent THAAD and other missile defenses from neutralizing a key power projection capability.

THAAD and other missile defenses also are a key element of the Pentagon’s new strategy of countering Chinese anti-access and area denial weapons, including the DF-21D, a unique, precision guided missile capable of sinking U.S. aircraft carriers more than 1,000 miles from Chinese coasts.

South Korea’s Joong Ang newspaper reported last month that Xi, the Chinese leader, urged Park in a prepared statement read during a closed-door meeting last July not to allow THAAD to be deployed. "If the United States attempts to deploy THAAD in the South Korean territory with the justification of protecting the American troops stationed here, South Korea, as a sovereign country, should exercise its right to express its opposition and the THAAD issue won’t be a problem between South Korea and China," Xi was quoted as saying. Chinese Foreign Ministry spokesmen did not deny that Xi made the statement and have repeated the government’s opposition to the missile defense system.

Xi’s reference to a future "problem" between the two countries is viewed by U.S. officials as a subtle threat to curb economic or trade relations.

Months after Xi’s appeal, Chang Wanquan, China’s minister of defense, visited South Korea in November. He told his South Korean counterpart, Han Min-koo, that China opposes deployment of THAAD .

Details of what trade and financial incentives China is offering the South Koreans if they agree not to deploy the missile defenses could not be learned.

However, South Korean investment in China has grown sharply over the past decade. From January to September last year, South Korea spent more than $3.2 billion in China, according to the Wall Street Journal. China also attracted large numbers of South Korean manufacturers and sent 25 percent of its $560 billion in total exports to China in 2013.

By contrast, South Korean exports to the United States have fallen sharply, from 40 percent of its total export market in the 1980s to 11 percent last year.

A senior South Korean official told the Journal that Seoul’s dilemma is that "China is our single most important economic partner. But we can’t weaken U.S. security ties."

Larry Wortzel, a former military intelligence officer once based in China, said the Park government is carefully managing ties with China while historical animosities have left Seoul leery of Japan.

"The Park government and the [Republic of Korea] armed forces are concerned over the missile threat from North Korea, but are wary of anti-ballistic missile systems that will link the U.S, ROK and Japan," Wortzel said. "These concerns have led successive ROK governments to be cautious about U.S-led anti-ballistic missile programs."

John Tkacik, a former offifical in the State Department, said that Beijing has been struggling in the campaign to split South Korea from its U.S. alliance.

The South Koreans "are very aware that Beijing's primary goal is to weaken U.S. security relationships in East Asia and isn't substantively committed to any real regional partnership with Seoul," Tkacik said, adding that Park appears to have a healthy skepticism of Beijing.

Still, large-scale South Korean investment in China brings risks of economic pressure from Beijing.

Gordon Chang, an economic affairs specialist on China, said Beijing’s policies typically involve "throwing lots of money at smaller countries and then treat[ing] them badly."

"At the moment, Chinese policymakers think they can point missiles at the South Koreans—directly and through North Korea—and then pay them enough so that they won’t take measures to defend themselves," Chang said. "It will be a neat trick if Beijing can pull this off. I suspect Seoul will take Chinese money for a few years and then decide to build its missile defenses anyway."

South Korea has said that it is planning its own version of a missile defense system, a system that could operate outside U.S. missile defenses in the region.

Alexandre Mansourov, a specialist at the Johns Hopkins University’s School of Advanced International Studies, said South Korea’s current infatuation with China "is transitory and will pass probably sooner than later."

"In the meantime, some adult supervision is in order, so that the ‘panda huggers’ in Seoul do not do any permanent damage to the ROK’s other core relationships and interests," he said.

"The U.S. government has not made final decisions regarding the permanent stationing of a U.S. THAAD unit in the Republic of Korea," said Chris Bush, a spokesman for U.S. Forces Korea.

Chun Hye-ran, South Korea’s presidential spokeswoman, had no immediate comment.

A Chinese government spokesman could not be reached for comment.

Hong Lei, the spokesman for China’s ministry of foreign affairs, has stopped short of directly opposing deployment of THAAD. "China holds a consistent and clear position on anti-missile issues," he told reporters in Beijing Feb. 5, when asked about Chinese concerns on missile defenses in South Korea. "It is our belief that every country should keep in mind other countries’ security interests and regional peace and stability while pursuing its own security interests."

"We hope that countries concerned can properly deal with relevant issues in the larger interests of regional peace and stability and bilateral relations," he said.

Months earlier, Hong was explicit in opposing missile defenses. "We think the antimissile deployment by certain countries isn't conducive to regional strategic stability and mutual trust," he said.