Attacks on opposition activists, firing of tear gas shells by police and arrests preceded the back-to-back 12-hour hartals today and tomorrow that the mainstream opposition parties enforce from six this morning.

Reports received from our correspondents in Sylhet, Satkhira and Mymensingh said over 50 people were injured when police and ruling BNP men attacked pre-hartal processions yesterday.

At least 20 people were injured as police resorted to lathi charge and fired tear gas shells and rubber bullets to disperse agitating AL activists at Tajpur Bazar under Osmani Nagar Thana in Sylhet yesterday afternoon, reports our staff correspondent in the district.

At 6:00pm, about 200 activists of AL and its front organisations brought out a procession at the bazar and police swung into action soon after.

Later, the activists held a protest rally at the bazaar with thana AL President Kabir Uddin Ahmed in the chair. General Secretary of thana AL Abdal Miah and other leaders addressed the rally, alleging police swooped on the peaceful procession.

A police however said police had to take action to bring the situation under control. Additional police force was sent to the bazar.

In Satkhira, at least 12 AL activists were injured as BNP workers attacked a pre-hartal procession in front of Kolaroa thana. They also ransacked thana AL office.

In Gouripur thana headquarters in Mymensingh, at least 10 people were injured as police and ruling party men swooped on a procession denouncing the grenade attacks in Dhaka and for drumming up support for the hartals.

Our Bogra correspondent reports, a police sub-inspector and eight others were injured when a cocktail was hurled on a procession of the AL and its front organisations at Sherpur.

Amidst an uneasy calm prevailing across the country since Saturday's incident, the government has beefed up security ahead of today's shutdown.

In the capital, 6,500 law enforcers will be deployed today instead of 5, 500 on other days.

In Chittagong, over 2,000 police men along with paramilitary Bangladesh Rifles and Armed Police Battalion personnel will be deployed in the port city today to maintain law and order, police officials said.

Special police teams have been posted and surveillance stepped up in and around all key point installations (KPIs) in the port city to avert violence.

"We have kept our men on high alert in this port city and we briefed our officials to be more vigilant," acting Commissioner of Chittagong Metropolitan Police Amjad Hossain told The Daily Star.

During an overnight special drive on Sunday, police arrested more than 140 people under Section 54 from different places of the port city.

Our staff correspondent in Khulna reports security measures have been further geared up in the city as panic gripped it ahead of the hartals. Ten platoons of police in riot gear have been deployed at the vulnerable points.

Local AL leaders held a rally yesterday, blaming anti-liberation forces for the grenade attack in Dhaka.

Khulna district and city units of the BNP in a joint statement yesterday condemned Saturday's incident.

Meanwhile, shop owners at a meeting with Sheikh Hasina yesterday extended their support to the hartal.

Shop Owners Association leaders including Amir Hossain and SA Kader met the opposition leader at her residence Sudha Sadan.

Usually, shop owners are opposed to hartals.

Other organisations which extended support to the hartal include Bangladesh Sarak Pari-bahan Sramik Union, Bangladesh Jubo Union, Chhatra Union, Bangladesh Krishak Sramik Mukti Andolon and Samajtantrik Sramik Jote.

Sammilito Sangskritik Jote will organise cultural functions today and tomorrow at 5:00pm at the Central Shaheed Minar, protesting the grenade attacks.