QUETTA, Pakistan - Militants in western Pakistan bombed a bus carrying women students on Saturday and then seized part of the hospital where survivors of the attack were taken, killing at least 21 people, officials said.

At least 27 were injured.

The gunmen in Quetta, the capital of Baluchistan province long plagued by sectarian violence, were holed up in the emergency ward of a hospital, engulfed in a firefight pitting them against the security forces.

Security forces had forced their way into part of the Bolan Medical Complex, where dozens of patients and staff were believed to be trapped. Television footage showed troops surrounding the building and a helicopter hovering overhead.

"They are several in number, we are still facing resistance from them, and people are stranded inside the hospital. We are trying our best to rescue the people," said Jan Mohammed Bulaidi, spokesman for Baluchistan's new chief minister, who took office last Sunday.

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