(Updates with death toll, details throughout)

ISLAMABAD, Nov 24 (Reuters) - Twin suicide blasts killed at least 16 people in the Pakistani garrison town of Rawalpindi adjoining Islamabad early on Saturday, the military said, including 15 aboard a defence ministry bus.

A suicide bomber rammed a car into the back of the bus outside an intelligence service office. Another bomber blew up his car at a checkpoint outside army headquarters.

The attacks come on the heels of a string of suicide bombings blamed on Islamist militants amid rising insurgency, and as Pakistan heads towards a general election in early January in political convulsions under emergency rule.

"Fifteen people were killed on the bus while three people were wounded in the suicide attack outside the general headquarters," army spokesman Major-General Waheed Arshad said. "Both were suicide attacks."

Officials had earlier reported that a security official was killed in the blast near army headquarters.

A Reuters witness saw the charred remains of the bus just inside the gate of the intelligence service compound in Rawalpindi, before police cordoned off the area and put up tents to obscure the view. (Reporting by Augustine Anthony and Zeeshan Haider; writing by Simon Gardner; editing by Roger Crabb)

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