At least 14 polling stations in Bangladesh have been set on fire, including one on the outskirts of the capital, Dhaka.
The wave of attacks came a day before voting began in the country's election.
On Friday, a busy commuter train was allegedly set on fire, killing four passengers.
Most opposition parties are boycotting the election, in which Prime Minister Sheikh Hasina is set to win a fourth consecutive term.
Police say a prominent opposition politician, Nabiullah Nabi of the Bangladesh Nationalist Party (BNP), and six other party activists have been arrested on suspicion of involvement in Friday's fire on a commuter train in central Dhaka.
Samanta Lal Sen, a senior official at the Dhaka hospital, says eight people have been critically injured.
Local media say a Buddhist temple in the south-eastern city of Chittagong has been torched, and the Election Commission says a local party office of the ruling Awami League has been attacked.
The BNP has asked voters to boycott the poll and called a two-day strike across the country.
The ruling Awami League has accused the BNP of trying to disrupt the election by unleashing a "reign of terror on innocent people."
On Friday, the UN Special Rapporteur, Clément Nyaletsossi Voule, said he was "deeply disturbed" by the repressive environment surrounding the polls.