The three lawyers including a British-trained female barrister were picked up in the capital Dhaka on Tuesday night by Bangladesh's Rapid Action Battalion (RAB), which is tasked with tackling militancy in the Muslim-majority nation.
Read: Bangladesh arrests Briton over blogger murders
"They were arrested for providing funding of 10.8 million taka ($135,000) to a new militant group called Shaheed Hamza Brigade in Chittagong," RAB spokesman Mufti Mahmud Khan told AFP.
The little-known group first emerged in April this year when the RAB arrested four alleged militants and seized arms and weapons including modern assault rifles at a hideout in Chittagong.
The RAB this week also detained three suspected militants over the murder of two prominent atheist bloggers, including a British citizen who police said was the "main planner".
Read: Bangladesh arrest suspected local militant chief
Four secular bloggers have been hacked to death in Bangladesh since the start of the year, sparking an international outcry and protests in the capital.
The government has vowed to hunt down the killers after facing accusations that too little was being done to stop such attacks.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ