SEOUL (Reuters) - A spokesman for North Korea s foreign ministry said on Thursday Pyongyang is not linked to any cyber attacks, the North s first response since the United States publicly blamed it for a massive worldwide cyber security breach.  As we have clearly stated on several occasions, we have nothing to do with cyber attack and we do not feel a need to respond, on a case-by-case basis, to such absurd allegations of the U.S.,  the spokesman said, according to the North s official KCNA news agency. The U.S. accusation was a serious political provocation against North Korea that Pyongyang would never tolerate, the spokesman said. The May cyber attack crippled hospitals, banks and other companies. 