"The government calls on Japanese nationals in the country's embassy in Seoul to be vigilant and on the South Korean government to boost security," Chief Cabinet Secretary Yoshihide Suga was quoted as saying by the NHK television.
Suga stressed that Japanese authorities strongly condemned the assault and urged for an investigation into the incident. There have been no reports that it was a terrorist attack.
Earlier on Thursday, a 55-year-old man attacked Lippert, slashing his face and left hand. The envoy has been delivered to a hospital for treatment. His wounds are reported as not life-threatening.
Reportedly, the attacker has a history of militant Korean nationalistic activism. He shouted for South and North Korea reunification and against joint annual military exercises by Seoul and Washington during the attack, according to media reports.
In 2010, the assailant was arrested for throwing pieces of concrete at the Japanese ambassador to South Korea.
