A little known Islamic group has claimed responsibility for the attack on the Marriott Hotel in Islamabad.
The hotel was hit by a suicide bomb which exploded killing more than 50 people and injuring 270, reported Radio Australia.
Dubai based Arabiya television says a group calling itself Fedayeen Islam or Partisans of Islam has called Arabiya's correspondent in the Pakistani capital, Islamabad.
The correspondent says he received a text message on his mobile phone showing a telephone number.
He says he called the number and then heard a recording in which the group admitted launching Saturday's attack.
The Arabiya television correspondent says the speaker spoke in English with a South Asian accent.
The Fedayeen Islam group has issued several demands including for Pakistan to stop its cooperation with the United States.