DHAKA - At least 11 people have been killed in local election-related violence in Bangladesh, seven of them shot dead by security forces, police said Wednesday as political crisis deepened.

The opposition said there had also been widespread vote-rigging in the elections for thousands of local councils across the country, which began on Tuesday and will run for four months.

Impoverished Bangladesh has been plagued by unrest since 2014 elections that the opposition boycotted and experts say the gridlock has led to a rise in radicalism in the conservative nation, which has seen a spate of killings of atheist bloggers, religious minorities and foreigners. Much of the latest violence was in the southern coastal town of Mathabria, where clashes broke out when thousands of ruling party supporters attacked police and border guards taking ballot boxes to the government headquarters.

"A magistrate ordered the shooting and officers fired at thousands of unruly people who attacked us with machetes, rocks and sticks," district police chief Walid Hossain told AFP. "Three people died on the spot and two on the way to hospital," he said, adding that another five people were hurt.

Another police official said all the victims were supporters of the ruling Awami League who had apparently attacked police fearing a local loss for their party.

Security forces also shot and killed two people in the southeastern coastal town of Sabrang when supporters of a rebel ruling party candidate tried to snatch ballot boxes from paramilitary forces, local police chief Kabir Hossain told AFP.

Four more died in other parts of the country as voting began Tuesday in the elections for more than 6,000 local councils across the country.

Even before the polls opened on Tuesday local media had reported that 10 more people had died in pre-election violence. A spokesman for the opposition BNP said there had been widespread rigging and fraud in the polls, including ballot-stuffing by ruling party supporters.

The BNP boycotted a general election in 2014 but returned to politics last year after three months of crippling protests failed to unseat the prime minister.

"They are holding another farcical election," party spokesman Ruhul Kabir Rizvi told AFP on Wednesday.

"Ruling party supporters controlled voting centres and stuffed ballot boxes even before the polls began. It's nothing short of vote stealing," he added.

Both the ruling party and the Election Commission said the polls had been fair.

But one independent election observer called the violence "unprecedented" and said as many as 3,000 people had been wounded in the run-up to the polls, a figure AFP could not immediately confirm.

"What we've learnt is that some 20 people were killed during election and pre-election violence and as many as 3,000 people were injured," said Abdul Alim, director of the independent Election Working Group which is funded by the US charity the Asia Foundation.

"Also a lot of ruling party candidates were elected unopposed, which is quite abnormal. "We suspect that they intimidated their rivals. Unfortunately, the Election Commission is reluctant to investigate these unopposed elections."

Bangladesh's Election Commission has faced criticism in the past and last year the main opposition party pulled out of mayoral elections saying the polls were rigged.

The council elections will be held in six phases and will not change the political landscape of the country, but a sweeping victory would consolidate Prime Minister Sheikh Hasina's hold on power.

Local newspapers said Hasina's Awami League had won more than two thirds of the councils in the first round of the polls.

Authorities were forced to suspend procedures in around 60 centres, but the election commission said the voting was largely fair.

"There were some stray incidents in some places," said chief election commissioner Kazir Rakibuddin Ahmed.

"There has been violence and irregularities. It was unfortunate."