The top U.S. intelligence official has said cyberterrorism is the leading worldwide threat to the country's security, Belfast Telegraph reported.

James Clapper is director of national intelligence and told Congress on Thursday, April 11 that cyberattacks and cyberspying can damage critical infrastructure like power grids.

But in prepared testimony, he said advanced cyber-actors like Russia and China are unlikely to launch such attacks unless they are threatened by conflict.

He gave examples like last year's denial-of-service attacks on websites for U.S. financial institutions, and the attack against 30,000 computers at Saudi oil company Aramco, as typical of what is to come.

Clapper also said al Qaida and its offshoots will continue to plot attacks on U.S. targets. He warned that the Arab Spring revolt has produced a spike in threats, and that Iran continues to present a danger.