At least 20 people were killed, including a police officer, while 33 were reported injured in a suicide blast at the Fatehpur shrine in Balochistan's Jhal Magsi district.
"A suicide bomber blew himself up after he was intercepted by police guards on duty outside the shrine, killing 18 people including three children under the age of 12 and two policemen, and wounding at least 27 others, 14 of them seriously," said Home Secretary Akbar Harifal.
Balochistan Home Minister Sarfaraz Bugti confirmed the toll.
Harifal added the seriously injured patients from the blast were being airlifted to Sindh in the absence of adequate medical facilities in Balochistan.
"A suicide bomber blew himself up after he was intercepted by police guards on duty outside the shrine," said Deputy Commissioner Asadullah Kakar.
"The suicide bomber struck outside the shrine at a time when it was packed with people, attending anniversary celebrations of Syed Cheesal Shah," Kakar added.
He also confirmed that one police constable was killed while attempting to stop the suicide bomber from entering the shrine.
The injured were transferred to DHQ hospital for treatment with the local administration declaring an emergency at hospitals in Sibbi and Dera Murad Jamali.
Balochistan Home Minister Sarfraz Bugti added that he had instructed concerned authorities to respond immediately to the incident.
Security forces reached the spot and cordoned the area after the incident.
Prime Minister Shahid Khaqan Abbasi has condemned the attack on the shrine. He said terrorists have no religion and the killers of Baloch people are enemies of the state.
The premier added that the state will respond with full force and will not allow terrorists to disturb the peace of the nation.
He also ordered the best possible medical care for the injured.
Earlier in February, at least 88 people were killed when a suicide bomber attacked the crowded Sufi shrine of Lal Shahbaz Qalandar in Sehwan, injuring up to 343 others.
In November 2016, at least 52 people including women and children were killed and more than 100 injured in a suicide blast in Shah Noorani shrine near Hub in Balochistan’s Lasbella district.
