Pakistan’s Prime Minister Nawaz Sharif waves to supporters casting his vote during a local government election in Lahore on Saturday.

Eleven people were killed when rival political parties fired on each other on Saturday as Pakistanis voted in local elections seen as a referendum on the national government halfway through its term.

The violence occurred in the Khairpur district of the southern province of Sindh, which held the polls along with the central Punjab province. It was not immediately clear which parties were responsible.

“Eleven people were killed when two groups opened fire,” police deputy inspector general Kamran Fazal told Reuters.

The opposition, led by international cricket star turned politician Imran Khan, is hoping the polls will help build a national coalition that could challenge Prime Minister Nawaz Sharif’s Pakistan Muslim League-Nawaz (PMLN) party at the next general election.

Pakistan’s other two provinces held their local elections months ago. Khan won in Khyber Pakhtunkhwa in the northwest and Sharif’s party and its coalition partners won in the sparsely populated western province of Baluchistan.

Observers are closely watching the polls in Punjab, Pakistan’s richest and most populous province and the power base of Sharif, who swept to national power in a landslide election in 2013.

“PMLN has the upper hand in Punjab but it will be a strongly challenged by PTI,” said political analyst Wajahat Masood, referring to Khan’s Pakistan Tehreek-i-Insaaf party.

Security and the economy have improved under Sharif but the government has failed to tackle corruption or tax dodging by the wealthy, two problems that are starving social services such as schools and hospitals of cash.

Over 20 million people are registered to vote in Punjab and 4.6 million in Sindh. Pakistan has a population of 190 million.

Local bodies, in which voters elect councillors directly, devolve administrative and financial powers to lower tiers of electoral bodies.

Local government elections were last held in 2005 under General Pervez Musharraf, who came to power in a bloodless coup.

National and provincial political parties dislike the system, saying the military has previously used it to undermine parliamentary democracy.

In March this year, the Supreme Court called the absence of the local government system for over a decade unconstitutional and ordered the election commission to arrange for polls to be held as soon as possible.

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