A former speaker of the U.S. House of Representatives says the biggest potential threat to U.S. national security consists of electromagnetic pulse attacks by North Korea, Russia and China.

Newt Gingrich made the remark during a special lecture he delivered at the Heritage Foundation in Washington on July 20th, local time.

In the speech, he expressed concerns about possible nuclear, electromagnetic pulse, biological and cyber weapons to which he said his nation remains susceptible.

Gingrich cautioned that the results could be devastating if the weapons were to hit their intended targets.

He added that the development of science and technology will further increase the probability of electromagnetic pulse attacks.

An electromagnetic pulse attack refers to a nuclear attack that simultaneously paralyzes power plants, automobiles and all electronic devices, causing an uncontrollable "blackout" of communications.