At least four persons died and more than fifty were reported injured when the 'Padmarag Express' slipped off the tracks in Gaibandha.
The Inter-city 'Meghna Express' in Chandpur and 'Nakshikantha Express' in Khulna derailed as fishplates of tracks were removed.
The derailments snapped Khulna and Chandpur's rail links with the rest of the country and also on the northern route of Lalmonirhat-Shantahar.
Railway officials said the sabotages took place between 1am and 6am Wednesday.
The railways have been particularly targeted during the serial back-to-back transport blockades by the Opposition over the past fortnight.
Dozens of incidents of sabotage have been reported from across the country, leading scores of derailment and huge delay in train services caused by suspension of services due to repairs.
Trains have also been attacked by Opposition activists and sometimes even set on fire.
Many have been injured in such incidents during the recent blockade but this is the first time people died.
Our correspondents report
4 die in Gaibandha
The 'Padmarag Express' derailed around 1.30am on Wednesday between the Bonarpara and Mahimaganj railway stations because fishplates and clips had been dismantled.
Bonarpara railway's station master Prasun Kumar Mandal said three coaches including the engine veered off the tracks.
One compartment was crushed and got stuck with the engine, leading to the deaths, he said.
Four bodies have been recovered till 10am, said Gaibandha Fire Service's deputy assistant director Kobbat Ali.
Bonarpara Railway Police OC Md Saidur Rahman said at least 50 others were injured.
"We have detained one Saddam Hossain and a Dudu Mia for the sabotage," said OC Rahman.
Fire service units from Gaibandha, Rangpur and Bogra's Sonatola and a rescue train from Bonarpara have reached the spot conducting the rescue operation.
Rescue workers said that a few passengers were stuck inside a coach and said more deaths could not be ruled out.
Train derails in Chandpur
The engine and two coaches of the 'Meghna Express' went off tracks as fishplates on the tracks at Shahtali in Chandpur had been removed.
Chandpur railway police OC Shubhash Kanti Das said the Chittagong bound train derailed around 5.30 am with more than 500 passengers.
"Casualties did not happen because the train was moving slowly. Services on Chandpur-Chittagong route have suspended since the incident," he said.
Trains will resume after the tracks between Chittagong and Laksham are cleared, Railway officials say.
Track sabotage in Khulna
Three coaches of the 'Nakshikantha Express' derailed as fishplates of tracks near the Bejerdanga rail station in Khulna's Fultola Upazila were removed.
Police said no casualties have been reported.
Railway Police OC Ekram Ali said that services between Khulna and rest of the country was snapped since 2am on Wednesday.
It might take until afternoon to resume train services because repairs and fixing the track will take a while, he said.
According to railway authorities seven trains are stuck in different stations of Khulna.