An Iraqi cameraman working for Reuters and held for three weeks without charge by the American military was released on Thursday, a US military spokesman said.
Ali al-Mashhadani, who also freelances for the BBC and US-based National Public Radio, was detained on July 30 in Baghdad's heavily fortified government compound, the Green Zone, during a routine check.
Reuters and the BBC welcomed his release, but called on the US authorities to explain why Mashhadani, who has been detained twice before, was held.
Major John Hall, a spokesman for the American forces in Iraq, said: "Just after noon he was turned over to Reuters. The findings of the investigation allowed him to be released."
The US military had earlier said it detained Mashhadani because "he has been assessed to be a threat to the security of Iraq and coalition forces." It declined to provide further details.
The cameraman's arrest was condemned by press watchdog groups and sparked calls for the US military to justify its actions.
The military says that under its UN mandate it can indefinitely hold anyone considered to be a security risk.
Mashhadani was detained by US forces before. He was held between August 2005 and January 2006 after footage and stills of Sunni insurgent activity in the western province of Anbar was found during a search of his cameras.
Later in 2006 he was held for another two weeks. On neither occasion were charges brought against him, according to Paris-based media watchdog Reporters Without Borders.
Reuters Editor-in-Chief David Schlesinger welcomed Mashhadani's release but voiced concern that it was the third time he was "detained without explanation."
"If there are legitimate issues about him or any other journalist, let's have them aired openly and tested. If there are none, let them pursue their profession free from intimidation and fear," he said, according to Thomson-Reuters' head office in London.
BBC News world editor Jon Williams added: "Ali is part of our Iraqi family -- his colleagues in London and Baghdad are delighted he's been freed.
"We now look to the American military authorities to offer evidence and an explanation for Ali's detention."
Ahmed Nouri, an Iraqi cameraman employed by the US news agency The Associated Press, was arrested by American troops on June 4 in Tikrit, and is still being held on security grounds at a base there.
