Cricket hero Imran Khan sworn in as Pakistan PM

Pakistan's World Cup cricket hero Imran Khan was sworn in as prime minister of Pakistan on Saturday, after promising a new era of responsibility and prosperity in a fighting speech in parliament.

Khan won a simple majority from lawmakers in a Friday confidence vote, three weeks after an election tainted by claims of military meddling and ballot-rigging.

Wearing traditional white shalwar kameez garments with a waistcoat, Khan stumbled over some of the words of his oath as he was sworn in.

The swearing in ceremony marks the end of decades of rotating leadership between two parties, punctuated by periods of military rule.

The July 25 election was branded "Pakistan's dirtiest", with accusations throughout the campaign that the military was trying to tilt the playing field in Khan's favour.

The army and Khan have denied claims from rival parties of "blatant" vote rigging.

The former cricketer, who captained Pakistan to World Cup victory in 1992, fell short of an outright majority, forcing him to partner with smaller parties and independents in order to form a government.

Khan and his Pakistan Tehreek-e-Insaf (PTI) party campaigned on promises to end widespread graft while building an "Islamic welfare state".

"First of all, we will start strict accountability. I promise to my God that everyone who looted this country will be made accountable," he said in his speech Friday.

PTI candidates were also voted speaker and deputy speaker of the National Assembly this week, putting Khan in a strong position to carry forward his legislative agenda.

He will face myriad challenges including militant extremism, water shortages, and a booming population negating growth in the developing country, among others.

Most pressing is a looming economic crisis, with speculation that Pakistan will have to seek a bailout from the International Monetary Fund.

Khan will also have to contend with the same issue as many predecessors: how to maintain a power balance in civil-military relations.

Khan, who captained Pakistan to their World Cup cricket victory in 1992, was dogged by the accusations he was benefiting from a "silent coup" by the generals which targeted the PML-N. Nawaz Sharif was ousted from power last year and jailed over a corruption conviction days before the vote, removing Khan's most dangerous rival.

In the West, Khan is often seen as a celebrity whose high-profile romances were tabloid fodder, but at home he cuts a more conservative persona as a devout Muslim who believes feminism has degraded motherhood.

Known to some in Pakistan as "Taliban Khan" for his calls to hold talks with insurgents, he increasingly catered to religious hardliners during the campaign, spurring fears his leadership could embolden extremists.