Pakistanis have labeled it a “selection” — not an election. Human rights monitors have condemned it as neither free nor fair.

As voters headed to the polls on Thursday, the influence of Pakistan’s powerful military and the turbulent state of its politics were on full display. Few doubted which party would come out on top, a reflection of the generals’ ultimate hold on Pakistan’s troubled democracy.

But the military is facing new challenges to its authority from a discontented public, making this an especially fraught moment in the nation’s history.

The tension was underlined on Thursday as Pakistan’s Interior Ministry announced that it was suspending mobile phone service across the country because of the security situation. Some analysts in Pakistan cast it as an effort to keep opposition voters from getting information or coordinating activities.

The election was taking place in the shadow of a monthslong military campaign to gut the party of former Prime Minister Imran Khan, a former international cricket star and populist leader who was ousted by Parliament in 2022 after falling out with the generals.

The crackdown is the latest dizzying swerve in the country’s roller-coaster politics.

The Pakistan Muslim League-Nawaz, or P.M.L.N., the party of the three-time former prime minister Nawaz Sharif, is expected to claim victory in Thursday’s vote. Mr. Sharif himself was ousted when he fell out of favor with the military in 2017, and Mr. Khan, with the military’s support, became prime minister a year later.

Now it is Mr. Khan who is sitting in jail after a bitter split with the military over its political control, while Mr. Sharif is apparently seen by the generals as the lone figure in Pakistan having the stature to compete with the widely popular Mr. Khan.

Voters will choose members of provincial legislatures and the country’s Parliament, which will appoint the next prime minister. It is seen as unlikely that any party will win an outright majority, meaning that the party with the largest share of seats would form a coalition government. Officially, this will be only the third democratic transition between civilian governments in Pakistan, a nuclear-armed nation of 240 million people.

On Thursday afternoon outside a polling station in Lahore’s Gawalmandi neighborhood, supporters of Mr. Khan’s party, Pakistan Tehreek-e-Insaf, or P.T.I., chatted as voters made their way through the winding alleyways of the old city and men smoked cigarettes on the balconies above.

The men complained that the mobile service outage had blocked them from using a P.T.I.-sponsored app to help them find their local polling station. The ballots were also particularly confusing, they said. While other parties use a single symbol to represent all their candidates, the authorities issued an individual symbol for every P.T.I. candidate — a move analysts said was designed to confound P.T.I. supporters.

“It was confusing even for me. There were so many symbols, it was hard to find the right one,” said Abdul Rashid, 60, a goldsmith, noting that he was literate, unlike many others in the country who need the ballot symbols to be able to identify their chosen party.

Earlier that morning, the police had threatened to arrest P.T.I. officials as they set up a booth near the polling station to provide information on candidates, according to one official, Muhammad Rafiq Gujjar, 52. The police also forced Mr. Gujjar to cover up all the photos of Mr. Khan at the booth, he said.

The military has ruled Pakistan directly through various coups or indirectly under civilian governments ever since the country gained independence in 1947. It has often meddled in election cycles to pave the way for its preferred candidates and to winnow the field of their competitors. But the military has used an especially heavy hand ahead of this vote, analysts say, a reflection of the growing anti-military fervor in the country stoked by Mr. Khan.

The crackdown has drawn widespread condemnation from local and international human rights groups. On Tuesday, the United Nations’ top human rights body expressed concern over “the pattern of harassment, arrests and prolonged detentions of leaders.”

“We deplore all acts of violence against political parties and candidates, and urge the authorities to uphold the fundamental freedoms necessary for an inclusive and meaningful democratic process,” Liz Throssell, spokeswoman for the U.N. high commissioner for human rights, said at a news conference.

The intimidation campaign has come at a particularly turbulent moment in Pakistan. For months after Mr. Khan was removed from office, he railed against the country’s generals and accused them of orchestrating his ouster — a claim they reject. His direct criticism of the military was unheard-of in Pakistan. It inspired his supporters to come out in droves to vent their anger at the military for its role in his removal.

“Imran Khan is a clearest case of political engineering gone wrong; the army became the victim of its own engineering,” said Zafarullah Khan, an Islamabad-based analyst. “Now civil-military relations are being written on the streets. This is unique in Pakistan.”

After violent protests broke out in May targeting military installations, the generals responded in force. Leaders of Mr. Khan’s party, P.T.I., were arrested and ordered to denounce the party. P.T.I. supporters were also swept up by the police. Mr. Khan was sentenced to a total of 34 years in prison after being convicted in four cases and barred from running in the election.

The authorities also allowed Mr. Khan’s rival Mr. Sharif, who had been living in exile for years, to return to the country. He quickly became a front-runner in the race after Pakistani courts overturned the corruption convictions that led to his ouster in 2017 and reversed his disqualification from competing in elections.

The military also sought a détente with Mr. Sharif, who has a loyal base of supporters in the country’s most populous province, Punjab, analysts say. The other major political party in Pakistan, the Pakistan People’s Party, or P.P.P., does not have nearly the same national appeal as P.M.L.N.

In Lahore’s Jain Mandir neighborhood, P.M.L.N. supporters gathered outside a tent that party leaders had set up to help supporters identify their polling station. Bright green and yellow banners with photos of Mr. Sharif and other party candidates hung over the crowd. Under the shade of the tarp, men took I.D. cards and handed voters a slip with their polling station and names of their local candidates.

Abdul Karim Butt, 75, sat in a chair, with green P.M.L.N. stickers and a golden pin of a tiger — the party’s symbol — decorating his brown scarf. Mr. Butt said he had supported Mr. Sharif since his first term in office, when he began to build a reputation in Punjab for reviving the economy and improving the province’s infrastructure.

“The work he did in Lahore no one else has done in history. He widened the roads, built many bridges. He changed the entire map of Lahore,” Mr. Butt said.

Mr. Sharif has also pushed for more civilian control of the government and had each of his terms cut short after falling out with the military — a history that raises doubts about how long this latest rapprochement with the generals will last.

While a P.M.L.N. victory appears certain, there are still some lingering questions about how the vote will play out. Some analysts believe that the military will not allow Mr. Sharif to become prime minister, given his contentious history with the generals. The military may instead seek to elevate his brother, former Prime Minister Shehbaz Sharif, who is much more deferential to the army but less popular with the public.

It is also possible that despite the crackdown, P.T.I. voters will come out in large numbers on Thursday, raising the possibility that the military could tamper with the vote count, the analysts said. If the military did so, that could spark protests.

The turmoil has laid out the dismal state of Pakistani politics, a winner-take-all game dominated by a handful of political dynasties and ultimately controlled by the military. In the country’s 76-year history, no prime minister has ever completed a term in office. This election is also the first in decades in which no party has campaigned on a platform of reforming that entrenched system.

“All mainstream political parties have accepted the military’s role in politics; there is no challenge,” said Mustafa Nawaz Kokhar, a former senator with the Pakistan People’s Party and a vocal critic of the military, who is running in the election as an independent candidate in Islamabad.

Salman Masood contributed reporting from Islamabad.