A bomb hidden under a seat ripped through a bus as it prepared to depart from a station in the restive Pakistani city of Hyderabad early Friday, killing at least two people and injuring nine, police and rescue officials said.

The bomb exploded at about 9:30 a.m. on a bus that was headed for the small town of Kotri, five miles to the west across the Indus River, said Naeem Ahmed, a spokesman for the EDHI Foundation, the city's emergency rescue organization.

The motive for the attack, near one of Hyderabad's main marketplaces, was not clear.

"We have two bodies of unidentified men and nine injured," Ahmed told The Associated Press. He said the injured were being brought to a local hospital.

The explosion came only hours after the execution in Virginia of Aimal Kasi, a Pakistani man convicted of the 1993 murders of two CIA employees, but there was no indication the two events were related.

Hyderabad, 95 miles west of the port city of Karachi, is a center of tension between the ethnic Muttahida Qami Movement and Sindhi nationalists, and has been plagued by violence. It was also the site of the trial of suspects in the murder of Wall Street Journal reporter Daniel Pearl. The convicted ringleader, Ahmed Omar Saeed Sheikh, is on death row at the Hyderabad jail pending an appeal.

On Sept. 15, a bomb exploded on a passenger bus in Hyderabad, killing one person and injuring two. No group claimed responsibility for that explosion.

The U.S. State Department has warned that Kasi's death for the CIA murders could result in retaliation against Americans around the world, and there have been protests in Pakistan leading up to his execution. Four Americans were gunned down in Karachi following Kasi's 1997 conviction.