The top U.S. diplomat in the six nation talks on the North Korean nuclear program says the United States and its allies will not accept a nuclear-armed North Korea.

Christopher Hill (file photo)

U.S. Assistant Secretary of State Chris Hill had a blunt warning for North Korea.

"It can have a future or it can have these weapons," said Chris Hill. "It cannot have both."

His comments came in response to Pyongyang's announcement Tuesday that it intends to conduct a nuclear test. Hill said the United States has been in close consultations with the four other countries involved in the six party talks - South Korea, China, Japan and Russia - and, in his words, "would have no choice but to act resolutely."

"I'm not prepared at this point to say what we're going to do," he said. "But I am prepared to say we are not going to live with a nuclear North Korea. We are not going to accept it."

Hill said the United States has received no response to a message passed to Pyongyang Tuesday through the North Korean mission to the United Nations. He said Washington is very concerned and believes a North Korean nuclear test would be, in his words, "a bad mistake."

"So, if what they have in mind is the notion that by somehow exploding this thing, they've created a fait accompli and we're just going to have to come to terms with a nuclear North Korea, they've got to think again," noted Christopher Hill. "We're not coming to terms with a nuclear North Korea."

The U.S. diplomat spoke at the inauguration of the U.S.-Korea Institute at Johns Hopkins University's School of Advanced International Studies. Hill is a former U.S. ambassador to South Korea, and he was joined by five other former U.S. envoys to Seoul.

Meanwhile, U.S. intelligence officials have detected what they are describing as unusual activity at potential North Korean nuclear test sites, although they have not been able to determine the nature of the activity.

North Korea gave no date for a prospective nuclear test, but has said it is necessary to counter perceived U.S. hostility. The United States has said it will not attack Pyongyang, and says there are significant economic and diplomatic benefits, if North Korea gives up its nuclear ambitions.