Islamabad, Pakistan - At least 14 people have been killed and more than 20 others wounded in a bomb attack on a mosque during sunset prayers in the southwest Pakistan city of Quetta.

"Currently we have 20 injured, and 14 people were killed," said Waseem Baig, spokesman for the city's main government hospital, where the casualties were taken on Friday.

"Eight people are critically injured."

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A senior police official, Amanullah, appeared to be the target of the bombing, and was killed in the attack, said police official Ali Muhammad.

Images from the scene showed rubble and debris strewn across the prayer courtyard of the mosque.

"We went to offer our prayers, when we went to bow our heads ... there was a sudden explosion," Azmatullah, a survivor of the attack, told Al Jazeera.

"I was near the door, so I ran from there to my home, which is nearby."

The attack is the second such incident to target security forces in Quetta this week.

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On Tuesday, at least two people were killed and more than 14 wounded after an improvised explosive device mounted on a motorcycle exploded in a market area.

That attack was claimed by Baloch separatist groups, who have been leading an armed uprising for independence for the ethnic Baloch areas of Balochistan province.

The province is Pakistan's largest and is rich in mineral resources, but its rugged terrain and arid climate also make it the country's least densely populated region.

No group immediately claimed responsibility for the attack on Friday.

"The roads are not safe anyway, but now we're not even safe in our mosques," said Azmatullah, who was wounded in Friday's bombing.

Asad Hashim is Al Jazeera's digital correspondent in Pakistan. He tweets @AsadHashim.