Korea's ruling Saenuri Party on Monday said "outsiders" were behind the violent protest against the prime minister in Seongju county last week, after the government announced it will deploy an advanced U.S. missile defense system there.

"Those that incite violent protests for a living should be punished," said Rep. Chung Jin-suk, the party whip. "We need to distinguish reasonable opinion-gathering of residents from the violence done by the outsiders."

Last week, angry protesters who opposed the deployment the Terminal High Altitude Area Defense in the southern town blocked Prime Minister Hwang Kyo-ahn's car for hours and threw water bottles and eggs at him, while he tried to explain the government's position on missile defense and alleviate health concerns expressed by locals.

Local investigators kicked off a probe centering on whether the residents violated protest-related laws and obstructed the premier from carrying out official duties.

The chief of a committee resisting the THAAD deployment in Seongju Lee Jae-bok earlier apologized to Hwang over the violence, saying the protest got out of hand as uninvited "outsiders" joined the crowd. He stressed that people living in the county will refrain from carrying out violent protests in the future.

Chung also claimed that unlawful protesters are also fueling discontent on other issues such as the Seoul-Washington free trade agreement, adding that the government must not sit idle and should deal firmly with such meddling.

Korean parties have been divided over the deployment of the THAAD in the country, with the opposition claiming that the move will hurt the diplomatic ties with Beijing and Moscow, while further provoke Pyongyang.

The government, however, maintains that the deployment is vital to better tackle North Korea's on-going nuclear and missile threats. (Yonhap)