Pamphlets of the Sindhu Desh Liberation Army (SDLA) claiming responsibility for the incident in revenge for the killing of Jeay Sindh Muttahida Mahaz leader Muzaffar Bhutto were found at the site of the attack in Nawabshah district of Sindh.
DSP Sardar Khan Chandio too told the media that the SDLA had claimed responsibility for the attack.
Nine people were killed and more than 30 others injured when gunmen fired at the passengers of the bus going from Karachi, the capital of Sindh, to Kohat in the country's northwest yesterday.
The Dawn newspaper said the attack was the first of its kind in Sindh.
Most of those killed in the attack were not residents of Sindh.
According to media reports, a man boarded the bus in Sakrand and said five companions would join him in Rein Shakh. At Rein Shakh, five armed men boarded the bus and asked Sindhi passengers to get off.
Soon after, the gunmen started firing at the passengers.
Pamphlets of the SDLA were found after railway tracks and branches of the National Bank of Pakistan in Sindh were targeted with low intensity bombs recently.
