South Korea has closed off the inter-Korean maritime border and forbidden North Korean ships from passing through South Korean waters as a follow-up to the sinking of the “Cheonan.”

A South Korean military official said that after the maritime border was closed off, the last of the three North Korean ships that were sailing in South Korean waters returned to North Korean waters at 11 a.m.

A Defense Ministry official said that no other North Korean ships have since approached South Korean territory.

The official added that a North Korean ship approached South Korean waters in the Yellow Sea on Tuesday night, but reversed its course after being warned by South Korean authorities.