Lahore, Apr. 23 : The United States is finding convincing Pakistan that the internal threat posed by extremism is a bigger threat to it than India, a "tough sell".

Delivering a lecture at the Harvard University, Central Command chief General David Petraeus said Islamabad must change its attitude towards New Delhi.

"The existential threat facing Pakistan is internal extremists and not India," The Daily Times quoted Petraeus, as saying.

Petraeus said India realizes that reducing tension with Pakistan is very necessary for regional peace, so Pakistan should also focus more on its efforts in fighting extremism inside its territory.

Meanwhile, addressing a US think tank, Senator Joseph Lieberman also highlighted the need for Islamabad to understand and realize who its real enemy was.

"Pakistanis have to understand that their major enemy in the region is no longer India, but its extremism. In fact, they have a common enemy in that with the Indians," Lieberman told Council on Foreign Relations.

However, Lieberman said that it was very difficult to make Pakistan accept the fact that it's internal problem is the root cause of all the trouble.

"That's a tough sell," he added. (ANI)