The US on Thursday said the Mumbai attacks had shown that Lashkar-e-Taeba was out to "fill the gap" created by a "diminished al-Qaeda" and a "decisive" action was needed from all countries of South Asia including Pakistan to defeat it.
US Coordinator on Counter-Terrorism Dan Benjamin said the aim of securing the world would remain incomplete unless LeT is defeated.
"I have said that we will not achieve our security aims if this group (LeT), with thousands of men under arms (is active)... We could see in Mumbai attacks, the target was set directly out of Bin Laden's book, filling the gap created by a diminished Al-Qaeda," Benjamin said at a function in New Delhi.
"We should be clear that terrorist threat in South Asia requires decisive counter-terrorism efforts by all countries of the region," Benjamin added.
He said his country was not just focussing on Al-Qaeda "but also against groups which are growing and have global reach like LeT".
The US official said the US and allied forces have made important gains against Al-Qaeda but socio-political and economic issues were to be addressed to counter the challenge thrown by terrorism.