"I found the letter at about 10:30am when I went into my room to check emails. I instantly informed the vice-chancellor about it," said Professor Sheikh Abdus Salam, chair of the department.

"In the next five days we -- the patriots -- (are) promising that we will bomb and destroy the entire Arts Building of the university ... ." the letter in English reads.

"We will gain it because we want a better life, a better country and an Islamic country. This bomb is capable of destroying half of this precious building. This bomb can be anywhere in the department waiting to blow. We are not monsters, we are doing this for future generation. Secondly, we will never be called terrorists ... we will be respected by people as great patriots. Your countdown is from the very moment," the letter says.

Vice-Chancellor Professor SMA Faiz told The Daily Star that the university filed a general diary and the police are keeping a close watch on the campus in the capital, still reeling from the August 21 grenade attack that killed 19 people.

"We have to unite against those who have been creating anarchy," Prof Faiz said adding: "We condemn the incident. I want cooperation from all to fight their evil design."

Earlier, an anonymous former officer of the National Security Intelligence wrote a letter to Professor Mohammad Akhteruzzaman, general secretary of Dhaka University Teachers' Association, alerting him to probable bomb attacks

"You should not join meetings, processions and namaz-e-janaza as they (fundamentalists) are targeting progressive people with car bombs," the letter says.

The letter referred to the killing of progressive, secular and intellectual people in 1971 and claimed that fundamentalists control all madrasas and 80 percent of schools and colleges and other institutions except for Dhaka University.

Akhteruzzaman told The Daily Star: "We cannot ignore it and there is no reason to take the matter lightly."