A special Bangladeshi tribunal sentenced seven of the eight suspects to death on Wednesday for their involvement in the 2016 Islamist attack on a Dhaka cafe that killed 20 people, including an Indian girl, the worst terror attack in the country's history.

"They shall be hanged by the neck until their death," Dhaka's Anti-Terrorism Special Tribunal judge Mojibur Rahman pronounced at the crowded court complex in Old Dhaka as the convicts appeared in the dock under heavy security.

The convicts were found to have financed, supplied weapons, or assisted those who directly took part in the attack on Holey Artisan Bakery in Dhaka's upmarket Gulshan area on July 1, 2016.

The judge acquitted the eighth suspect as the prosecution side could not prove his links to the attack by the outlawed Neo-Jamaatul Mujahideen Bangladesh (Neo-JMB).

Investigators earlier said that all the five neo-JMB operatives who directly took part in the attack were killed the next morning in a counter-assault by the military commandos.

The counter-attack, however, killed an employee of the bakery and fatally wounded another who succumbed to his wounds two days later.

The 17 foreigners killed in the attack included nine Italians, seven Japanese, one Indian girl. Two Bangladeshi police officers were also killed during the siege.

The Indian girl, Tarishi Jain, a student of the University of California in Berkeley, was among those killed in the attack. She was in Dhaka on vacation.

The judge in his verdict identified Bangladeshi Canadian Tamim Chowdhury as the mastermind of the attack, who later was killed during a nationwide anti-militancy security clampdown.

The verdict simultaneously observed that Chowdhury tried to draw Islamic State (IS) support to militant attacks in Bangladesh.

The IS had immediately claimed responsibility of the Holey Artisan attack and several other subsequent militant assaults in the country.

But Bangladesh repeatedly declined the presence of any foreign terrorist group in the country attributing the incidents to homegrown terrorists.

Security analysts and officials, however, said several Bangladeshi homegrown militant groups were in touch with or influenced by international terrorist outfits.

The trial in the case started after the Counter-Terrorism and Transnational Crime unit submitted a charge-sheet on July 23, 2018, after two years of investigation.