Washington: Insisting upon the fact that Pakistan must keep its commitments to root out the "cancer of violent extremism", President Barack Obama on Thursday asserted US will never tolerate a safe haven for those who aim to kill Americans.

"No country is more endangered by the presence of violent extremists," Obama said referring to Pakistan.

In a televised speech on troops withdrawal plans from Afghanistan, he said, "We will work with the Pakistani government to root out the cancer of violent extremism and we will insist that it keep its commitments."

The US President sent out a blunt message that the US was ready to launch more direct assaults on safe havens harbouring terrorists who wanted to target Americans.

"For there should be no doubt that so long as I am President, the United States will never tolerate a safe haven for those who aim to kill us: they cannot elude us, nor  escape the justice they deserve," Obama said.

Obama's comments came in the midst of festering strains in ties between the US and Pakistan following the unilateral American action that killed al-Qaeda chief Osama bin Laden in his hideout in Abbottabad, near Islamabad, last month.

He made it clear that Washington will "continue to press Islamabad to expand its participation in securing a more peaceful future for the war-torn region."

Obama announced details of the withdrawal of 33,000 US troops from Afghanistan by the summer of 2012.

Before his speech, Obama and his Pakistani counterpart Asif Ali Zardari, in a telephonic conversation, had agreed to take "appropriate steps" to repair relations between the two countries, which were affected by last month's covert American raid that killed bin Laden.

(Agencies)