The United States will likely launch pre-emptive strikes on perceived cyber threats, U.S. Defence Secretary Leon Panetta said on Thursday, underscoring the emerging shift of international conflict to the digital arena.

"If we detect an imminent threat of attack that will cause significant physical destruction in the United States or kill American citizens, we need to have the option to take action against those who would attack us," Mr Panetta was reported by Reuters as saying in his speech before a business forum in Washington.

The American defence chief, at the same time, called on business leaders to ramp up their efforts of establishing respectable security firewalls in light of the rising online security breaches in the past years that exposed the vulnerabilities of major global firms and even key government agencies around the world.

U.S. firms in particular, Mr Panetta added, were deemed by cyber warfare experts as lacking preparedness to effectively ward off future attacks.

In reality, the top American defence official noted that "too few companies have invested in even basic cyber security."

Mr Panetta warned that threats are for real and intruders possess the tools, resources and capabilities to barge into targeted systems and networks, both government and private, and "cause panic, and destruction, and even the loss of life."

Security analysts have long argued that sophisticated hackers, possibly backed by governments, can spread destruction simply by dispatching rogue computer programs that can infect computer systems without much of a challenge.

Attacks could include the disruption of public transport systems and other important infrastructures such as a nation's water reservoir and power grids, Mr Panetta said.

U.S. intelligence reports have been floating suspects that would be the logical source of future attacks, which in the case of the U.S. government would likely emanate from China, Russia and Iran, Reuters said.

While not pinpointing on specific sources, Mr Panetta warned: "Potential aggressors should be aware that the United States has the capacity to locate them and to hold them accountable for actions that may try to harm America."

The U.S. defence chief, however, clarified that Pentagon would only resort to such actions "under certain and dire scenario."

He admitted too that at the moment, the U.S. military lacks the congressional framework to formally beef up America's ability to counter cyber threats but this issue will likely be filled in by an executive order coming from the White House.

But in the next seven years, Pentagon would have finalised a definite blueprint on how to conduct cyberwarfare with aggressive entities, Mr Panetta said.