Seoul has instructed its foreign embassies to take extra precautions against possible North Korean attempts to kidnap or attack South Koreans abroad, officials said Monday.

The instruction was issued in response to North Korea's threat to retaliate for last month's group defection by 13 North Koreans, who Pyongyang says were kidnapped by South Korean spies while working at a North Korea-owned restaurant in China.

South Korea's Unification Ministry spokesman Jeong Joon Hee reiterated Monday the 13 North Koreans decided on their own to resettle in the South. He said South Korea keeps close tabs on possible North Korean responses like an attempt to abduct or attack South Korean citizens in foreign countries.

The Foreign Ministry said it has instructed its overseas diplomatic facilities to be extra careful about the safety of its personnel and South Koreans staying abroad. It didn't elaborate.

Defections are a contentious issue for the rival Koreas. More 29,000 North Koreans have fled to South Korea since the end of the 1950-53 Korean War, according to South Korean records. South Koreans defecting to the impoverished, authoritarian North is rare.

The recent defection of a male restaurant manager and 12 female workers is the biggest group defection by North Koreans to South Korea since North Korean leader Kim Jong Un took power in late 2011.