|US retaliation for cyber-attacks could take many forms|
The US is working on a plan to categorise cyber-attacks as acts of war, says the New York Times newspaper.
In future, a US president could consider economic sanctions, cyber-retaliation or a military strike if key US computer systems were attacked, officials have said recently.
The planning was given added urgency by a cyber-attack last month on the defence contractor, Lockheed Martin.
A new report from the Pentagon is due out in a matter of weeks.
"A response to a cyber-incident or attack on the US would not necessarily be a cyber-response. All appropriate options would be on the table," Pentagon spokesman Colonel Dave Lapan told reporters on Tuesday.
'All necessary means'
The Pentagon's planning follows an international strategy statement on cyber-security, issued by the White House on 16 May.
The US would "respond to hostile acts in cyberspace as we would to any other threat to our country", stated the White House in plain terms.
"We reserve the right to use all necessary means - diplomatic, informational, military, and economic - as appropriate and consistent with applicable international law, in order to defend our nation, our allies, our partners and our interests."
The strategy will classify major cyber-attacks as acts of war, paving the way for possible military retaliation, reported The Wall Street Journal after interviewing defence officials.
Sophistication of hackers
One of the difficulties strategists are grappling with is how to track down reliably the cyber-attackers who deliberately obscure the origin of their incursions.
And it is not clear how the Pentagon proposes to deal with cyber-attackers, such as terrorists, who are not acting for a nation state.
The sophistication of hackers and frequency of the attacks came back into focus after an attack on arms-maker Lockheed Martin on 21 May.
Lockheed said the "tenacious" cyber-attack on its network was part of a pattern of attacks on it from around the world.
The US defence department estimates that more than 100 foreign intelligence organizations have attempted to break into American networks.