Bangladesh has arrested 14 of the 26 men deported from Singapore on terror charges and released the remaining 12, who are being monitored by police.

The Singapore authorities had arrested the 26 men, most of them construction workers, after discovering that they were planning terror attacks in their own country.

The 14 men were charged last month under the Anti-Terrorism Act after they returned to Bangladesh, Dhaka police officials said. Under the Act, the maximum punishment is the death sentence.

On Dec 27, they appeared in a Dhaka court, which ordered them to be detained in jail while investigations took place.

"The 14 are now in jail... investigations are going on. The rest have been released to their relatives under some conditions. They are being monitored," Dhaka Metropolitan Police spokesman Maruf Hossain Sorder told The Straits Times. "They don't have any previous record."

Police investigations showed that the men were from different parts of Bangladesh and got to know each other while working in Singapore.

The men were part of a closed religious study group that had met discreetly every week since 2013, according to Singapore's Home Affairs Ministry.

Mr Mashrukur Rahman Khaled, a deputy commissioner with the Dhaka police, said the men were influenced by the Ansarullah Bangla Team (ABT), also known as Ansar Bangla, an extremist organisation in Bangladesh.

The ABT has been accused of being behind a series of gruesome killings of atheist bloggers.

Bangladesh has seen a rise in extremist violence in recent years, marked by the high-profile murders of four bloggers, one publisher and two foreign nationals over the past 12 months alone.

Analysts see the development as a cause for concern for Bangladesh in its fight to stamp out terror.

"How deeply they were committed and how they were in possession of whatever evidence was found by Singapore. This is a matter for investigators to come up with (answers)," said Mr Tariq Karim, a former Bangladeshi diplomat and a distinguished fellow with the Delhi-based Vivekananda International Foundation.

"Certainly this should be worrying for any country and any government."