A North Korean newsreader announces the country is ready to launch a merciless attack against the United States, potentially involving a "diversified nuclear strike."

The Thursday declaration comes as the North barred staff from the South from entering a joint-industrial park for a second day, causing tensions between the two to climb sharply.

Businesses operating in the Kaesong industrial zone held a news conference, claiming the North has demanded South Korean operations pull out by April.

South officials contend the report is distorted, despite the fact the North has threatened to shut the park, which generates $2 billion a year in trade .

There are 828 South Korean workers still in the zone.

But just 222 had indicated they wanted to return to South Korea on Thursday, with the rest trying to keep their factories running.

Should a conflict spark they risk to become potential hostages.

Japanese officials have condemned what it sees as the Nort