A correspondent for American network CBS News was critically injured and her two-man British film crew were killed in one of the bloodiest days in Iraq for several weeks.

Kimberly Dozier, 39, was filming at a roadside when a bomb was detonated. Veteran cameraman Paul Douglas and soundman James Brolan, both London-based, were killed.

Dozier was rushed to a US military hospital where she underwent emergency surgery. Doctors said that they were optimistic although the reporter remains in a critical condition.

The crew had been working as embedded reporters within the 4th Infantry Division of the US Army. A US Army Captain and an Iraqi interpreter accompanying the film crew were also killed in the attack.

Authorities said that the explosion happened just before noon local time in Tahariyat Square, a mixed area in south-central Baghdad. The blast collapsed the front end of their armoured Humvee.

Douglas, 48, was an experienced cameraman who had worked for CBS News since the early 1990s, covering conflicts in Iraq, Afghanistan, Pakistan, Rwanda and Bosnia.

Brolan, 42, had spent 12 months working as a freelancer for the organisation in Baghdad and Afghanistan. He was part of the CBS News team that had received a 2006 Overseas Press Club Award for its reporting on the Pakistan earthquake.

A spokesman for the Foreign Office said: "We can confirm that two British journalists working as part of the CBS news crew were killed in an attack on a convoy in Baghdad this morning.

"A US army captain and an Iraqi interpreter were also killed in the incident. A US journalist was injured and is in a serious condition." The spokesman said that next of kin had been informed and consular staff in Baghdad were providing assistance to the families.

Before she was stationed in Iraq three years ago, Dozier worked as the London bureau chief for CBS News. She also anchored the foreign affairs programme World Update on the BBC's World Service, and had won three American Women in Radio and Television Gracie Awards for reports from the Middle East, Kosovo and Aghanistan.

Sean McManus, President of CBS News and Sport, paid tribute to Douglas and Brolan as "invaluable" journalists.

"This is a devastating loss for CBS News," he said. "Kimberly, Paul and James were veterans of war coverage who proved their bravery and dedication every single day.

"They always volunteered for dangerous assignments and were invaluable in our attempt to report the news to the American public. Our deepest sympathy goes out to the families of Paul and James, and we are hoping and praying for a complete recovery by Kimberly.

"Countless men and women put their lives on the line, day in and day out, in Iraq and other dangerous spots around the world, and they deserve our utmost respect and gratitude for the work they do."

More than 70 foreign and Iraqi journalists have been reported killed since the US-led invasion in March 2003. This does not include the many translators, drivers and other assistants said to have died since the conflict began.

Today's violence saw at least 51 people killed across Iraq in a slew of violent attacks.

In the single most devastating incident, 11 bus passengers were killed and 16 wounded when a bomb inside a bus exploded in the small town of Khalis, 60 miles north of Baghdad. Most of the dead were exiled Iranians who opposed the regime in Tehran, prompting accusations that the Iran government may have ordered the bombing.

Eight people were killed and nine injured when a roadside bomb exploded in a Shia district in the north-west of the capital.

Twelve people were killed and 24 were wounded, most of them university students, when a car bomb targeting an Iraqi army patrol detonated in Adhamiya district, northern Baghdad. In the same district another car bomb exploded near the Abu Hanifa Sunni mosque, killing five people and wounding seven, and prompting an exchange of fire between insurgents and the Iraqi army.

One person was killed and two others wounded when a roadside bomb went off near a minibus in southwestern Baghdad, police said.

Police patrols were targeted by car bombs, roadside explosives and gun ambushes throughout Baghdad, killing six and wounding five more.

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