The US Peace Corps has suspended its activities in Bangladesh indefinitely for fear that Americans may become the targets of Islamic militants.
Bangladesh recently arrested several top leaders of the JMB
A spokeswoman said all 70 volunteers had now left the country. Bangladesh said the move was "ill-advised".
The decision follows the arrest of militants blamed for a series of bomb attacks. Peace Corps fears retaliatory attacks by "terrorist elements".
The US on Tuesday expressed support for anti-terrorism actions in Bangladesh.
In the past few weeks security forces have arrested five of the top seven leaders of the banned Jamaat-ul-Mujahideen Bangladesh (JMB).
US PEACE CORPS
Movement officially founded in 1961
Proposed by John F Kennedy to encourage US citizens to volunteer in developing nations
Mission to create world peace and friendship
More than 182,000 volunteers have worked in 138 countries
Projects include teaching English, HIV/Aids education and development work
The group's chief, Abdur Rahman, was seized two weeks ago in the north-eastern town of Sylhet. His deputy, Siddiqul Islam, better known as Bangla Bhai, was captured four days later.
The JMB's alleged top bomb-maker also died in a blast during an operation by security forces on Monday in the eastern town of Comilla, the BBC's Waliur Rahman in Dhaka says.
The government blames the JMB for bombings which have claimed nearly 30 lives since last August.
US Peace Corps press director Barbara Daly told the BBC News website that the safety and security of its volunteers had to be the organisation's "number one priority".
The Peace Corps based its decision to pull out on a thorough assessment of the current environment, she said, rather than any specific threat.
Abdur Rahman is the chief of the banned JMB
In a statement released by the US embassy in Dhaka, the Peace Corps hailed the capture of the top militants as a significant step forward in the campaign against terrorism and extremism.
"Ironically, one consequence of that success is concern over possible reprisal attacks against Americans or other Western nationals by JMB activists still at large," the statement said.
Ms Daly said the security situation in Bangladesh would be periodically reviewed to determine whether the suspension should continue.
"We would love to return to Bangladesh but we just have to wait for the environment to be the right one before we do so," she added.
Bangladeshi Foreign Secretary Hemayet Uddin said the Peace Corps' decision to pull its personnel out of Bangladesh on security grounds was surprising.
Bangladesh has provided full security to foreigners living there and none have been targeted by Islamic militants, he told the BBC.
"It is an ill-advised decision and there is no reason to do it," he said.
Since returning to Bangladesh in 1998 after a 30-year gap, Peace Corps volunteers have worked chiefly in education and youth development.
The movement traces its roots back to 1960, when John F Kennedy - then a US senator - called on university students to serve their country in the cause of peace by volunteering around the world.
It was officially founded a year later, with the mission of creating world peace and friendship.
The Peace Corps periodically pulls out of countries because of safety concerns caused by political unrest or natural disaster.
Nepal, Uzbekistan, Haiti and hurricane-affected Caribbean nations are among those to see volunteers withdraw in recent years.