The US Assistant Secretary of State, Christina Rocca, has called for more religious and political tolerance after meeting top politicians in Bangladesh.
Ms Rocca said the opposition leader should be better protected
Speaking in Dhaka, Ms Rocca said the government needed fully to investigate recent acts of political violence.
More then 100 people have been killed in opposition rallies and cultural activities in recent years.
During her visit, Ms Rocca met the prime minister, foreign minister and the main opposition leader.
She said that Washington condemned extra-judicial killings, and hoped that the perpetrators will be brought to justice.
Human rights groups have accused an elite anti-crime squad - the Rapid Action Battalion in Bangladesh of killing at least 80 suspects either during capture or in custody during an anti-crime drive in 2004.
The government has promised to investigate the claims.
"We have seen steps recently in the right direction toward improving law and order.
"But our position is very clear - incidents of extra-judicial killings are not acceptable," Ms Rocca said.
She said that she supported the government's recent move in banning two Muslim extremist groups.
"We encourage all governments to go after extremists and terrorists," she said.
Ms Rocca also called on the government to provide better protection to opposition leader Sheikh Hasina.
She said the US was willing to provide technical assistance to the police force of Bangladesh and other law enforcing agencies.
She also urged the government to ensure tolerance and protection of minorities, following recent attacks on the minority Muslim Ahmadiyya sect.
"We hope Bangladesh's tradition of tolerance and moderation will continue," she said.
Ms Rocca is on the last leg of a week-long tour of South Asia that has included India and Nepal.
Her trip marks the first high-level US visit to Bangladesh since President Bush was re-elected last November.