South Korea has revealed for the first time what sanctions it will take against the North following its nuclear test earlier this month.
N Korea said the South could pay dearly for imposing sanctions
Unification Minister Lee Jong-seok said some Northern officials would be banned from the South under new travel rules.
He also said that Seoul would tightly control inter-Korean trade.
The announcement came despite a warning from North Korea that sanctions imposed by Seoul would be seen as an act of confrontation.
South Korea has been hesitant to take strong measures against the North because of its proximity, as well as close cultural ties.
The UN Security Council approved new arms and financial sanctions against North Korea following its nuclear test on 9 October.
Member countries are currently debating how to enforce these restrictions, with the US and Japan urging other nations to fully comply with the agreed terms.
NEW UN SANCTIONS
Bans sale to, or export from, N Korea of military hardware
Bans sale or export of nuclear and missile related items
Bans sale of luxury goods
Freezes finances and bans travel of anyone involved in nuclear, missile programmes
Allows inspection of cargo to and from N Korea
Stresses new resolution needed for further action
The Security Council has called on all members to state how they plan to implement sanctions by mid-November.
US Secretary of State Condoleezza Rice acknowledged on Wednesday that applying restrictions on Pyongyang involved "a complicated set of issues for South Korea", but again urged Seoul to show a strong commitment to the sanctions.
The US is likely to welcome Mr Lee's announcement of action against the North.
Mr Lee said Seoul would enforce UN travel restrictions on North Korean officials, and added that the government would vet all financial transactions related to inter-Korean trade.
In addition, he said North Korean ships arriving in South Korean ports would be subject to a more rigorous customs check.
But he added that existing inter-Korean economic projects, involving a joint industrial complex and a tourism zone in North Korea, would continue.
The government in Seoul has argued that these projects do not fall under the UN Security Council's resolution forbidding the transfer of material, equipment, and financial resources that may benefit North Korea's nuclear programme.
Act of 'confrontation'
Seoul's announcement came just a day after the North gave its first warning specifically directed at the South.
"If the South Korean authorities end up joining US-led moves to sanction and stifle, we will regard it as a declaration of confrontation against its own people ... and take corresponding measures," the North said in a statement.
US President George W Bush recently accused North Korea of trying to "test the will" of the five nations negotiating with it over its nuclear programme - the US, South Korea, Japan, China and Russia.
"The leader of North Korea likes to threaten," Mr Bush said.