China recently summoned South Korea's ambassador to receive the government's official protest over the country's request for a U.S. missile shield, The Telegraph reported.
The Chinese government fears that a regional neighbor having an advanced anti-missile system, such as the U.S.'s Terminal High-Altitude Area Defence (THAAD) system, will "compromise the effectiveness of its own nuclear deterrent," the report said.
Previously, South Korea has only been considering the said request, as it received concerns over antagonizing China. Nonetheless, it was forced to come up with its final decision when North Korea held its latest missile test, after four earlier nuclear tests.
South Korean President Park Geun-hye announced on Sunday that they would ask the U.S. about the "earliest possible" arrival of the THAAD missile defense batteries.
"The security of South Korea and its people are under threat as nobody knows the reckless provocations that North Korea will make," Park said during a meeting of the National Security Council on Sunday.
Apart from the compromise in China's missile capacities, the Chinese government is also wary of a possible recovery of the U.S.'s influence in South Korea. China has been intensively wooing the country over the last two years.
Despite China's objection, South Korea is adamant that the THAAD is only a defensive system rather than an offensive weapon. It is designed to destroy forthcoming ballistic missiles.
According to experts, South Korea's inevitable decision was prompted by North Korea's regular conduct of nuclear weapon and ballistic missile tests.
Defense consultancy IHS Aerospace affiliate Ben Goodlad told to Agence France Press that "the nuclear testing coupled with the testing of ballistic missile technology was always likely to strengthen the argument that South Korea needs to bolster its missile defenses."
An additional concern is North Korea's plan to carry out yet another underground nuclear test. In case, it would be the fifth detonation the country will undertake in a decade.
North Korea has been receiving condemnation for its latest provocations, even from its old allies like Russia and China.