SEOUL, South Korea (AP) — North Korea said today it will end a diplomatic communication channel with the United States and hinted at harsher punishment for Americans detained in the country in retaliation for U.S. sanctions that target leader Kim Jong Un.

The U.S. government last week imposed penalties on Kim and 10 other top officials for alleged human rights abuses. North Korea is already sanctioned because of its nuclear weapons program, but it was the first time that Kim has been personally sanctioned. The North called the sanctions tantamount to a war declaration.

Today, the North’s state media said it told the United States it will terminate contact through a U.N. channel in New York that allowed diplomats to communicate.

The New York channel refers to a method for North Korea’s U.N. diplomats to communicate with U.S. diplomats in New York. This is needed because the countries don’t have diplomatic ties and their animosities have deepened because of the North’s nuclear and missile programs.