SEOUL - A fresh wave of cyber attacks that slowed U.S. and South Korean websites this week hit more targets on Thursday, a web security firm said.

The South's spy agency has said the hacking may be linked to North Korea.

The anticipated attack did take place, but considerable counter measures were taken and it did act as a defense to some degree, an official at the online security firm Ahnlab said.

Some government websites including the Defense Ministry and the National Intelligence Service have been affected. Access to some U.S. government sites, including the State and Defense Department, from South Korea appeared to be disabled.

The Internet sites of some South Korean banks also experienced a surge in access request but a bank official said programmes were run to disperse traffic and bring service back up within an hour.

(Reporting by Jack Kim and Rhee So-eui; Editing by Jeremy Laurence)