"The injuries to the remaining two soldiers do not appear to be life threatening, however they and the coalition national who was seriously wounded, continue to be closely monitored," he said.

Awarded medals for his service

Signaller McCarthy was born on January 5, 1983 in Auckland, New Zealand.

He enlisted into the Australian Defence Force on the July 10, 2001. After initial recruit training and completion of mandatory courses, Sean posted to 7 Sig Regt on July 14, 2003.

He was posted to SASR on January 15, 2007.

His operational service included deploying as part of the Special Operations Task Group (SOTG V) in 2007; Operation Astute in East Timor in 2008 before redeploying to Afghanistan as part of his most recent deployment, the defence force said.

For his service in East Timor and Afghanistan, signaller McCarthy was awarded the Australian Defence Medal, the International Coalition Against Terrorism Clasp, the Afghanistan Campaign Medal, the NATO Medal and the Return from Active Service Badge.

Signaller McCarthy was the recipient of a SOCAUST commendation awarded on June 20, 2008 for his actions in Afghanistan in 2007 as part of SOTG Rotation V. Sean was awarded this for his excellent application of battle craft in a complex, dangerous and confusing situation, the defence force said.

He was not married.

Air Marshal Houston extended his sympathy to the man's parents, who are currently travelling in Europe.

"My heart goes out to them at this terrible time," he said. "Though I cannot ease their grief, I want them to know, they are in our thoughts and prayers."

Air Chief Marshal Houston described McCarthy as an experienced, highly skilled and professional soldier, who was well respected by his peers. He was a keen rugby union supporter who would be missed by his many friends.

Rudd: fear more lives will be lost

The Prime Minister Kevin Rudd said this morning from Japan that he feared more lives would be lost in the conflict in Afghanistan, after describing as a tragedy the latest fatality.

"Sean McCarthy was a fine Australian soldier in the best traditions of the Australian Defence Force,'' Mr Rudd said from Sapporo, where he is attending the G8 summit of world leaders.

"He had been commended for his previous active service on two overseas deployments, one also in Afghanistan, and the other in East Timor.

"Sean McCarthy is a terrible loss to his family, a terrible loss to the ADF, a terrible loss to the Australian nation.

"My thoughts, my prayers and the deepest thoughts and prayers of the Australian nation and people go to his family and loved ones.''

Mr Rudd said the ADF mission in Afghanistan was difficult, dangerous and bloody, adding: "We have lost Australian forces before and my fear is that we will lose them again.''

Hardening the soldiers' resolve

Air Chief Marshal Houston said Signalman McCarthy's death would strengthen the resolve of Australian forces to "go after" the Taliban bombmakers.

The roadside bomb, so-called improvised explosive device, which hit the vehicle McCarthy and three others were in, now accounted of 70 per cent of casualties in Afghanistan.

The latest attack brings to six deaths and a total of 40 casualties incurred by Australian forces in Afghanistan.

The attack will "harden our resolve'' to target the Taliban bombmakers, Air Chief Marshal Angus Houston said.

However, he said he was "very happy'' that Australian forces in Afghanistan were achieveing their objectives. in the province of Oruzgan, Australian forces had extended their area of influence, pushing back Taliban forces, he said.

"This loss will be a trigger for more actions and operations against the people who produce these dreadful weapons,'' Air Chief Marshal Houston said.

Strengthening insurgency

Today's news comes amidst one of the bloodiest periods in the conflict, due a strengthening Taliban insurgency.

More American and coalition-led troops have died in the last month than in any other month since the war began in 2001.

The US army lost 46 soldiers in the month of June, 15 more than it lost during the same period in Iraq. At least 13 British soldiers were killed in the same period.

Three days ago, the single biggest attack in the Afghan capital took place, when a suicide bomber drove an explosives-filled car into the gates of the Indian embassy, killing 41 people.

The attack came two days after an American air strike reportedly killed at least 27 civilians at a wedding party, most of them women and children. US forces have disputed that figure, arguing no women or children were killed and that only militants were killed in the attack.

The strengthening of the Taliban insurgency over the past several years has been marked by an increase in roadside bomb attacks, like the one that killed Signaller McCarthy.

Pentagon figures show that between 2006 and 2007 the incidence of roadside bomb atttacks rose from from 1931 in 2006 to 2615 in 2007.

with Mark Davis in Sapporo