The war of words between North Korea and the United States could make them look "stupid," Egyptian billionaire Naguib Sawiris told CNBC exclusively on Thursday.

Sawiris, who owns a telecom company in North Korea, told CNBC that wars are not won with rhetoric.

"If you threaten and you don't act you really look stupid, so it's best not to," Sawiris said in an exclusive interview.

In the latest row between North Korea and the United States, Pyongyang threatened Thursday to sink Japan and said the U.S. should be "beaten to death like a rabid dog."

The comments followed fresh sanctions from the United Nations on North Korea, which were approved by consensus earlier this week. This is now the ninth sanctions package that the UN security council has approved since 2006 for North Korea's missile tests.