ISLAMABAD (AFP) - Mr Imran Khan's party said it has begun talks with independents and small parties to form a coalition government after a resounding triumph in Pakistan's general election, as rival parties planned protests over alleged vote rigging.

Mr Khan's Pakistan Tehreek-e-Insaf party (PTI) won 115 seats in Wednesday's (July 25) ballot, short of the 137 needed for a simple majority, but a surprisingly strong showing that helped fuel suspicion of rigging.

The party has begun reaching out to potential coalition partners to form a government, according to spokesman Fawad Chaudhry, a task that analysts said should be straightforward.

"We have contacted small parties and independent members, they will soon meet party leaders in Islamabad," Mr Chaudhry announced late on Friday, adding that the process was likely to take about 10 days.

Mr Chaudhry's comments followed an announcement by rival parties vowing to launch a protest "movement", after foreign observers voiced concerns about the contest.

More than a dozen parties calling themselves the All Parties Conference (APC) promised to protest over the results.

However, the group remained divided, with some parties pledging to boycott joining the National Assembly and others calling for a new vote.

The outgoing Pakistan Muslim League-Nawaz party announced its support for the group, but stopped short of saying it would boycott the new Parliament.

And the Pakistan People's Party (PPP), which was notably absent from the APC, said in a separate announcement that it rejected the results, but vowed to try to convince the other parties to participate in the parliamentary process.

The protests announcement late on Friday came as the United States, the European Union and other observers voiced concerns over widespread claims that the powerful military had tried to fix the playing field in Mr Khan's favour.

Mr Khan's victory represents an end to decades of rotating leadership between the PML-N and the Pakistan PPP that was punctuated by periods of military rule.

The vote was meant to be a rare democratic transition in the Muslim country, which has been ruled by the powerful army for roughly half its history.

But it was marred by violence and allegations of military interference in the months leading up to the vote, with Mr Khan seen as the beneficiary.

The former cricket star will face myriad challenges, including militant extremism, an economic crisis with speculation that Pakistan will have to seek a bailout from the International Monetary Fund, water shortages and a booming population.