The announcement, carried on the KCNA state news agency, said the North was cancelling all non-aggression pacts with the South and closing the main Panmunjom border crossing inside the Demilitarized Zone.
It also said it was notifying the South that it was "immediately" cutting off the North-South hotline – a hotline installed in 1971 and intended as a means of direct communication at a time of high tension.
In the run up to the UN vote on Thursday, Pyongyang issued a series of warnings and in the hours before the council met it raised the threat of a pre-emptive nuclear strike on the United States.
The US said it took the threats seriously, but that "extreme rhetoric" was not unusual.
"One has to take what any government says seriously," State Department spokeswoman Victoria Nuland said of the nuclear threat.
"It is for that reason that I repeat here that we are fully capable of defending the United States. But I would also say that this kind of extreme rhetoric has not been unusual for this regime, unfortunately."
South Korean defence ministry spokesman Kim Min-seok warned that if the North were to carry out a nuclear attack it would become "extinct from the Earth by the will of mankind".
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