People attend a rally to protest against deploying the U.S. missile defense system, called Terminal High Altitude Area Defense (THAAD), in front of the defense ministry in Seoul, South Korea, July 13, 2016. South Korea's defense ministry on Wednesday announced an agreement with the United States to deploy the U.S. missile defense system, called Terminal High Altitude Area Defense (THAAD), to its southeastern region despite continued opposition from neighboring countries. [Photo: Xinhua/Wang Jiahui]

South Korea's main opposition Minjoo Party of Korea, the MPK, has defended a trip to Beijing by some of its members, saying the visit has helped bilateral diplomatic relations.

It comes after a group of MPK lawmakers visited Beijing earlier this week to discuss the controversial deployment by South Korea and America of the THAAD - Terminal High-Altitude Area Defense system on the Korean Peninsula.

In response, South Korean President Park Geun-hye criticized the visit for deepening internal divide in the country.

She called the ruling and opposition parties to unite as one and to place their trust in the government.

The THAAD deployment decision has strained relations between South Korea and its neighbors China and Russia.

But Park's ruling Saenuri Party claims the THAAD deployment is an issue of national security and doesn't need parliamentary approval.

South Korea has seen a number of protests recently against the THAAD deployment, particularly by those living in Seongju county, where the first battery of the system is to be installed next year.