Bangladesh police raided hotels, conducted random checks of people on the street and detained about 25 people across the country to try to thwart more attacks after a wave of bombings, officials said on Wednesday.
More than 500 bombs went off across the country on August 17, killing two people and wounding about 100, in a co-ordinated attack blamed on a banned Islamic party.
US Charge d'Affaires in Dhaka, Judith A. Chammas, met Foreign Minister M. Morshed Khan on Wednesday and said America wanted to help Bangladesh hunt the perpetrators of last month's blasts and prevent future attacks.
"We discussed possible ways of providing assistance...and how we could be helpful to Bangladesh," Chammas told reporters after the meeting, adding that the image of Bangladesh would be questioned abroad following the blasts. No one has claimed responsibility for the August 17 attacks, but leaflets found at most bomb sites carried a call by banned Islamic militant group Jamaat-ul-Mujahideen for the introduction of Islamic rule in Bangladesh, a Muslim democratic country.
State Minister for Home (Interior) Affairs Lutfuzzaman Babar said last week he believed not only Islamic militants but other radical elements were also involved in the August bombings, and that the government was taking precautions.
The elite Rapid Action Battalion of the police, using sniffer dogs and metal detectors, searched cars and pedestrians in the streets, especially near Dhaka's diplomatic areas, on Wednesday.
Security was tightened at airports, rail stations and ferry terminals.
Police said 25 people were taken into custody nation-wide on Tuesday on suspicion of being militants, but 18 were later released.
Authorities said the measures were being taken as a general precaution against further attacks but they had no specific information that any were being planned. Police have arrested about 200 people in connection with the attacks.
"Many among those arrested have confessed to being members of the Jamaat-ul-Mujahideen and being involved in the blasts," a police officer said on Wednesday.
Police have yet to find Jamaat-ul-Mujahideen's supreme leader and suspected mastermind of the attacks, Shayek Abdur Rahman, who is believed to have fled the country along with close associates.
Police said they also were looking for leaders and activists of Janajuddha, a leftist radical group that is believed to have helped in carrying out the August 17 blasts.