UPDATE 2-Little-known Islamic group claims Pakistan attack

(Adds quotes, details from tape)

DUBAI, Sept 22 (Reuters) - A little known Islamic group claimed responsibility for Saturday's suicide attack on the Marriott Hotel in Islamabad which killed 53, Al Arabiya television reported on Monday.

The group calling itself Fedayeen Islam (Partisans of Islam) demanded the closure of U.S. and NATO military bases in the region and the U.S. embassy in Pakistan, and an end to U.S. attacks against tribal areas in Pakistan and Afghanistan.

"If these demands are not met, we are ready to die," said a spokesman for the group on an audio tape aired by Arabiya. The Dubai-based television station said the English-language recording had been played over the phone to its correspondent in the Pakistani capital.

The speaker said the group had targeted 250 U.S. Marines and NATO officials which he said had been at the hotel, and warned of new attacks, urging Muslims to keep away from places frequented by Westerners.

Arabiya said the authenticity of the tape could not be verified, and the group is not known to have claimed other attacks.

The Czech ambassador and at least three other foreigners were among the 53 people killed in the blast, Islamabad's worst bomb attack. The truck bombing wounded 266 people and security officials said it bore the hallmarks of al Qaeda.

"The purpose of this (attack) was to kick the American crusaders of out Pakistan and to stop them from interfering in government, military, media, security, religious and other important institutions of Pakistan," said the speaker whose voice was distorted to make it unrecognisable.

The group also demanded an end to U.S.-Pakistani military cooperation and the release of militants it said were being held in U.S. "secrets prisons", including Sept. 11 mastermind Khaled Sheikh Mohammed, and Afifa Siddiqui, a Pakistani woman on trial in the United States for suspected links to al Qaeda. (Reporting by Firouz Sedarat; Editing by Matthew Jones)