Prime Minister Lee Wan-koo expressed regret over the shocking attack on U.S. Ambassador to Seoul Mark Lippert on Thursday, ordering diplomatic efforts to prevent any negative impact on bilateral relations.

Progressive activist Kim Ki-jong, 55, cut Lippert's face and wrist with a 25-centimeter knife as the U.S. official was preparing to give a lecture at a breakfast function in central Seoul.

Lippert is now recovering in stable condition at a hospital after undergoing surgery.

The assailant, who has been arrested, later said he launched the attack to end the annual joint Seoul-Washington military exercises, which he said hamper efforts to reunify two Koreas.

"It is regrettable that an incident like this took place," Prime Minister Lee Wan-koo said of the attack. He ordered the utmost efforts for the Lippert's treatment.

The prime minister also directed Vice Foreign Minister Cho Tae-yong to "promptly explain the latest incident to the U.S. and prevent (occurrences of) any problems in the cooperation with the U.S. (due to the attack)," according to Lee's office.

Lee also urged tighter protection and security for foreign emissaries and embassy facilities in the country.

In an emergency meeting of vice ministers from the home affairs, foreign affairs, justice and public safety ministries held later in the day, officials resolved to hand out stern punishment to those who failed to ensure the safety of the ambassador.

The government also decided in the meeting to muster more diplomatic efforts to prevent any negative impact in the bilateral ties while bolstering bodyguard efforts for foreign envoys and their embassies, according to the prime minister's office. (Yonhap)