Peshawar, Pakistan (CNN) -- At least 12 people have been killed in a multiple bombing Tuesday afternoon at a movie theater in Pakistan's northwestern city of Peshawar, a hospital official said.
Syed Jamil Shah, press officer for the city's Lady Reading Hospital, said at least 17 others were injured.
A senior Peshawar police officer, Ijaz Ahmed, said three hand grenades hit the Shama Cinema, which is infamous in the city for showing pornographic movies.
One blast was inside the cinema, and the other two outside, he told reporters.
The movie theater had received security threats, and police had advised that metal detectors should be set up outside it. This advice was not heeded, Ahmed said.
A witness, Waliur Rehman, told CNN he was watching a film when the blast rocked the building. People started running outside.
"There was a cloud of dust and smoke," he said. "The first blast was followed by another -- and then another -- explosion."
No group or individual has claimed responsibility for the attack.
Shahidullah Shahid, spokesman for the Pakistan Taliban, also known as Tehreek e Taliban Pakistan, denied any involvement by the militant group.
Peshawar, the capital city of Khyber Pakhtunkhwa province in northwest Pakistan, borders the tribal districts that are a stronghold of the Pakistan Taliban.
A week ago a suicide bomber blew himself up near a hotel restaurant in Peshawar, killing nine people and injuring more than 30 others, according to local officials.
Journalist Zahir Shah Sherazi reported from Peshawar, and Laura Smith-Spark wrote in London. CNN's Sophia Saifi contributed to this report from Islamabad, Pakistan.