Islamabad, Pakistan(CNN) Pakistan's election commission is expected to confirm former cricket star Imran Khan's victory Friday after polls marred by widespread allegations of vote-rigging.

According to early results, Khan's center-right Pakistan Tehreek-e-Insaf (PTI) has been swept to power, gaining an unexpectedly strong mandate, but failing to win a majority in the National Assembly.

In the latest official count, Khan's party had won 115 seats out of a potential 270 seats, with 267 having been declared.

Analysts said Khan had sufficient numbers to form a government with independent national assembly members and small regional numbers, without needing to team up with extremist religious parties as some had feared.

"This is an exceptional result in so far that all surveys and analysis had predicted a hung parliament and a messy coalition government," said Umair Javed, an academic and political commentator.

Rigging accusations

The apparent victory of the 65-year-old populist, who campaigned as a "change" candidate bent on building a "new Pakistan," has widely been trumpeted as historic for breaking the two-party duopoly that has dominated national politics for decades.

Banking on his huge popularity as a sports celebrity and the PTI's success as a regional party, his anti-graft mantra struck a chord with disenchanted young and middle-class Pakistanis.

However, the delayed election results have intensified cries of foul play after every political party except Khan's alleged ballot-rigging. Some claim their monitors did not receive final counts or were asked to leave polling stations before tallying was finished.

"If they take to the streets, then there could be considerable unrest," said Michael Kugelman, South Asia expert at the US-based Wilson Center.

"Given that seemingly every Pakistani political party other than the PTI has alleged fraud, there could be quite a few people on the streets."

Speaking before the final result was announced on Friday afternoon, Michael Gahler, the chief observer from the European Parliament, said there had been a systematic effort to undermine the ruling party.

Asked about reports of vote-rigging, Gahler urged "those who wish to contest results to do so through legal channels."

The vote -- only the second democratic transition in Pakistan's 71-year history -- was also overshadowed by hundreds of political arrests, a massive crackdown on the media and increasing tensions over allegations that the powerful military covertly backed Khan.

Former Prime Minister Nawaz Sharif was ousted from office last year over corruption-related charges, which led to his imprisonment earlier this month.

Sharif's brother, Shahbaz, leader of the incumbent Pakistan Muslim League-N (PML-N), said on Twitter there had been "massive rigging" in Khan's favor.

The leader of the Pakistan People's Party (PPP), Bilawal Bhutto Zardari, son of the late leader Benazir Bhutto, also took to Twitter to say he would reject the results over concerns of ballot-rigging, saying it was "inexcusable (and) outrageous."

Supporters of Pakistani cricket star-turned-politician and head of the Pakistan Tehreek-e-Insaf (PTI) Imran Khan, cheer and wave flags during a rally during the last campaign day, in Lahore, on July 23, 2018.

Possible protests

Analysts said that tensions may mount if international organizations that monitored the election cast aspersions on the vote's integrity.

The European Union's monitoring team handed down a preliminary assessment of the elections on Friday, saying that positive changes to the legal framework were overshadowed by restrictions on freedom of expression and unequal campaign opportunities.

US State Department spokeswoman Heather Nauert said in a statement Friday that the US concurred with the EU observers, and shared concerns expressed by the Human Rights Commission of Pakistan over flaws in the pre-voting electoral process. But Nauert added that the US would look for opportunities to work with elected leaders "to advance our goals of security, stability, and prosperity in South Asia."

Parties who have rejected the vote also convened Friday to agree on a joint strategy, and called for demonstrations.

"Allegations of procedural irregularities in the post polling phase by several parties need to be investigated," said columnist Mosharraf Zaidi, adding that the election commission needed to explain the delay in announcements of results, particularly in Karachi, Pakistan's largest city, where the results bucked expectations.

Claims of election rigging are commonplace in Pakistan. In 2014, thousands of Khan's supporters marched on the capital Islamabad to demand Nawaz Sharif's resignation amid claims of vote-rigging during the previous year's general elections.

They staged a four-month protest, which analysts said enjoyed the sympathy of the army, which wanted to hamper Sharif's rule.

"The military is unlikely to back the opposition this time around, and if domestic and international observers conclude that it was a fair election, opposition momentum will lose steam," said Javed.

Javed said that Khan may also avoid a political stand-off by negotiating with the parties. PML-N members may barter in return for a reduction of the 10-year prison sentence handed to Nawaz Sharif, he said.

The PPP, meanwhile, will be likely muted because it needs government spending to implement its agenda in its Sindh province stronghold, added Javed.

Supporters of Pakistan's cricketer-turned politician Imran Khan, head of the Pakistan Tehreek-e-Insaf (Movement for Justice) party, celebrate during general election in Lahore on July 25, 2018.

Guarded optimism

Opposition to the result may be limited as well because Khan's declaration of victory was greeted with optimism by many in Pakistan.

Khan was widely credited with having given a statesman's performance that set aside partisan rivalry and called for unity in facing Pakistan's looming economic crisis.

Dawn newspaper, which bore much of the brunt of the pre-election media crackdown, urged a cross-party reconciliation.

"Imran Khan's acceptance speech yesterday was an encouraging sign," it said in an editorial. "Opposition parties should route their complaints and protests through official channels."

Many are prepared to give a Khan administration a fair chance. Nadir Cheema, a London-based academic, said that even though he opposed PTI's conservative politics and its links with the military establishment, he would respect the results.

"Despite the pre-poll rigging, intimidation and an unleveled playing field, I support the weakest form of democracy," rather than none at all, he said.

The leader of the next government of Pakistan, an Islamic republic of 207 million people, will have to deal with a massive debt crisis and a febrile political atmosphere.

The nuclear-armed state also faces uncertainty over its relationships with the United States -- which has cut military aid due to Islamabad's alleged support for the Taliban in neighboring Afghanistan -- and China, which has financed multibillion-dollar infrastructure projects in the South Asian country.