MASTUNG (Balochistan) • Pakistan was in shock yesterday after a suicide blast killed more than 130 people, shaking confidence in security just as the dramatic arrest of former prime minister Nawaz Sharif ratcheted political tensions higher ahead of nationwide polls.

Sharif's highly anticipated return from London and subsequent arrest for corruption was overshadowed as the carnage in Mastung, in the south-western province of Balochistan, unfolded late Friday.

Newspapers branded the blast - one of the deadliest in Pakistan's history - a "massacre", as analysts and the media called on the military to prevent such attacks.

One week ago, Sharif was sentenced in absentia to 10 years in prison on corruption charges.

He was transferred to the garrison city of Rawalpindi, adjacent to Islamabad, after landing in Lahore last Friday.

Media reports said he was being held in a prison there.

Sharif has claimed he is the victim of a military conspiracy, and there are widespread allegations from the media, politicians and analysts that the powerful security establishment is meddling in the polls.

Mobile signals were blocked and police were deployed in the eastern city of Lahore where Sharif's supporters had gathered as he landed.

Soon after, the scale of the destruction in Mastung - hundreds of kilometres to the south-west, where an Islamic State in Iraq and Syria suicide bomber attacked a crowded political rally - began to emerge.

"It has never been more true that Pakistan's security establishment needs to focus on security, not politics," tweeted analyst Mosharraf Zaidi as mourners gathered to bury their dead in Mastung yesterday.

Provincial Home Secretary Haider Shako added that extra security forces had been deployed in "sensitive areas" and warned politicians to be alert.

AGENCE FRANCE-PRESSE