The use of military force against al-Qaeda is not restricted only to hot battlefields like Afghanistan, Brennan declared in a lecture at the Harvard law school, adding that US can take pre-emptive action against suspects who pose an imminent threat to it, anywhere in the world.
Laying out what he called the Osama bin Laden raid doctrine, Brennan said that under international law US has the right to take pre-emptive action whenever it foresaw any threat to it, the New York Times reported.
Brennan said America's anti-terror campaign must go beyond Afghanistan, but legal curbs could out constraints.
America's right to unilateral action, he said, does not mean that US would use military force indiscriminately.
"International legal principles including respect for states'' sovereignty impose constraints on our ability.
The paper quoted official as saying that Obama team was divided on the legal leeway the US had in killing Islamists militants in Yemen and Somalia.
NYT said the discussions pivotal to the future course of anti-terror fight centred on the extent to which Washington could escalate drone strikes, cruise missiles or commando raids from current high-value al-Qaeda targets to hit thousands of extremists foot soldiers.
Brennan also sharply criticised a proposal in the Senate version of the 2012 defence authorisation bill that would require terrorism suspects arrested inside the US to be transferred to military custody. Calling the idea a non-starter, he said, the White House would fight the proposal vigorously.