U.S. President Barack Obama Sunday described Pakistan as a "strategically important" ally for his country and said Washington and Islamabad have been working together to eradicate extremism which is a "cancer".

"Pakistan is an enormous country. Strategically important country not only for the U.S. but for the world... a country that has enormous potential but it also has some of the extremist elements. The Pakistani government is aware of that (extremism) and what we have tried to do is to engage aggressively with them," Obama told Indian students during an interaction at St Xavier's College here. "To communicate with them that we want nothing more than a stable, prosperous and peaceful Pakistan, and that we will work with the Pakistani government in order to eradicate this extremism that we consider a cancer," Obama said.

On Indian-Pakistani relations, the U.S. President said: "The history between India and Pakistan has been incredibly complex and was born of much tragedy and much violence."

"India and Pakistan can prosper and live side by side, this will not happen tomorrow but needs to be the ultimate goal. The U. S. can be a partner but can't impose this process. India and Pakistan have their own understanding," he said.