The North has denied any responsibility for the sinking of the Cheonan in the Yellow Sea near the maritime border in March 2010. Forty-six sailors died.
The South Korea spokesman, Kim Hyung-suk, said the sanctions were "aimed at making clear to the North they will be made to pay for provocations and ... taken because Seoul had no choice," the Yonhap news agency reported.
"In the spirit of correcting the wrong they committed, the communist country must make the first move [to show remorse] that can be accepted by the South Korean public," Kim said.
The sanctions banned all North Korean ships from entering South Korean waters and ended cross-border trade. Visits to the North by South Koreans were prohibited and new investments and assistance programs with the North were stopped.
Closing of the jointly operated Kaesong industrial complex just over the border in North Korea was not included in the sanctions. In April, North Korea ordered l 53,000 workers to leave the complex, resulting in its shutdown.
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