Japan, fearing it could be a soft target for possible North Korean cyberattacks in the escalating row over the Sony Pictures hack, has begun working to ensure its basic infrastructure will remain safe and to formulate its diplomatic response, officials said.

The hacking of the U.S. unit of Tokyo-based Sony Corp. has been seen in Japan largely as an American problem, but the officials said the government is now moving actively to confront the issue after U.S. President Barack Obama blamed North Korea and vowed to respond "in a place and time and manner that we choose."

Cyberdefense experts, diplomats and policymakers worked through the weekend at Prime Minister Shinzo Abe's office to launch the effort, said one official involved in the process.