Washington: While condemning the deadly suicide attack on worshippers at a mosque in Pakistan as "deplorable violence", the US has said it continues to stand by Islamabad in its efforts against those seeking to undermine democracy and freedom.

 Through their violent actions,terrorists continue to demonstrate "blatant disregard" for the efforts of the Pakistani people to build a more peaceful and prosperous country in which citizens are free to worship, Secretary of State Hillary Clinton said.

Her comments came Saturday evening hours after a teenage suicide bomber blew  himself  up at a mosque packed with hundreds of worshippers in Khyber tribal region of northwest Pakistan on the third Friday of the holy fasting month of Ramzan, killing 53 people and injuring 123 others.

"The United States strongly condemns the attack on scores of innocent Pakistanis in northwest Pakistan. The slaughter of worshipers as they gathered at a mosque for Raman's Friday prayers underscores the brutality of those who target civilians during celebrations and a reflection for Muslims throughout the world," Clinton said in a statement.

"Our thoughts and prayers are with the families and loved ones affected by this deplorable violence," she said.

She said the United States deeply respects Pakistan's sacrifices in the fight against ongoing extremism and continues to "stand with Pakistan against those who seek to undermine democracy and freedom."

In New York,UN chief Ban Ki-moon said the world body is with Pakistan in its efforts to tackle terrorism.

Ban is"appalled at this deliberate attack at a place of worship ... and the reported use of a teenager to perpetrate the attack," a statement by his spokesperson said.