Senator Edward Kennedy, Senator John Kerry and Rep. Barney Frank took the move after Nazli Kibria, a professor at Boston University and daughter of SAMS Kibria, met Congressman Barney Frank (D-MA) recently to discuss her father's assassination.

The three American lawmakers sent the letters to the US State Department and the Bangladesh embassy in Washington, DC, expressing their "strong concern over the recent wave of political terrorism in Bangladesh", according to a press release made available to the news agency.

"As tensions rise in the lead up to an expected general election in 2006, political violence has escalated sharply in Bangladesh," says the release quoting the letters.

They noted that at an opposition political rally in Dhaka last August, grenades were hurled at the opposition leader and former prime minister, Sheikh Hasina, in an "attempted assassination" which killed 22. The violence culminated in the recent grenade blast that killed five opposition Awami League members and led to a series of countrywide strikes called by the Awami League in February.

In their letters to Secretary of State Condoleezza Rice and Bangladesh Ambassador to the US Shamsher M Chowdhury, the legislators urged a fully independent investigation by the FBI aimed at helping to bring the perpetrators to justice, said the press release issued by Congressman Barney Frank on April 1 in Washington.

In their letters to the Bangladesh ambassador, they said, "This latest grenade attack is part of an escalating wave of political violence in recent years against moderate forces in Bangladesh, and it appears to us that the permissiveness of at least some within the Bangladesh government and the police in allowing violent groups to operate unconstrained, and the apparent failure to investigate previous similar attacks, led to a climate of impunity that encourages a continuation of such violence."

Immediately after the attack, the State Department strongly condemned the bomb attack, and the Bangladesh government subsequently sought assistance from the US in investigating the incident.

According to the State Department, the United States wanted to make sure the FBI would have full access to all evidence and witnesses before committing to an investigation. The State Department has since signalled that the FBI is assisting in the investigation, "though it's unclear the degree to which the FBI is able to investigate with full authority and to work without interference".

In their letters to Secretary of State Rice, the legislators pointed to the recent State Department's human rights report on Bangladesh, which describes "frequent government use of police for political purposes".

The release on the letters continued, "The report also describes an increase in the number of killings by security personnel, in which nearly all abuses went uninvestigated and unpunished, which creates a serious obstacle to ending this kind of political violence. Because this pattern of political terrorism goes counter to basic democratic principles, we strongly urge you to make it clear to the Bangladesh government that an independent investigation by the FBI is essential if we are to maintain our longstanding supportive bilateral relations with their country."

They noted although Bangladesh government reportedly charged several low-ranking activists of the ruling Bangladesh Nationalist Party in recent days, Asma Kibria, the widow of Shah AMS Kibria, and opposition party leaders questioned the impartiality and thoroughness of the investigation, particularly in light of the fact that the government has refused to make the findings public.