Pakistan has been hit by violence on the day of its general elections – with at least 31 dead in the worst attack.

A suicide bomber blew himself up outside a polling station in the city of Quetta. The Islamic State group said it had carried out the attack.

Elsewhere, minor blasts and clashes left several injured and two dead.

Millions have voted in the polls, with the parties of ex-cricket star Imran Khan and disgraced former PM Nawaz Sharif competing for the most seats.

Voting officially closed at 18:00 (13:00 GMT), with the results probably known early on Thursday.

The campaign has been overshadowed by concerns of fraud and violence, and the Human Rights Commission of Pakistan says there have been “blatant” attempts to manipulate the polls.

Mr Khan has vowed to tackle corruption but his rivals accuse him of benefiting from alleged meddling by the military, which has ruled Pakistan for nearly half of its history.

Mr Sharif, who won the last election, has been jailed for corruption after a scandal stemming from the Panama Papers leak.

Despite tight security, with hundreds of thousands of troops and police officers deployed across the country, there have been violent attacks. In addition to the suicide attack in Quetta, in Balochistan province, one person died in a grenade attack in Khuzdar, and another died in a shooting between political rivals in Swabi, Khyber Pakhtunkhwa province.

The Dawn newspaper also reported clashes in Mardan, Rajanpur, Khipro and Kohistan.

In an interview on Monday, Mr Sharif’s daughter Maryam Nawaz – who was jailed earlier this month with her father on corruption-related charges – criticised the military. “When a prime minister refuses to put down his head and do their [the military’s] bidding, they pull him down with four things; get a religious fatwa issued against him, call him a traitor, call him a friend of India, or call him corrupt. They use these things against every elected prime minister,” she said.

Several PML-N candidates also say they have been coerced to switch to the PTI. The Pakistani military denies interfering in politics.

Independent media, meanwhile, say there have been blatant attempts to muzzle them. There are also concerns about the participation of militants on international terror blacklists in the election process.

For all these reasons, the human rights commission has said there are “ample grounds” to question the legitimacy of the polls, “with alarming implications for Pakistan’s transition to an effective democracy”.