US Defence Secretary Donald Rumsfeld has pledged to personally sign letters of condolence to the families of American soldiers killed in action.

He spoke shortly after his admission that he had used a machine to sign letters to relatives of more than 1,000 troops killed in Iraq and Afghanistan.

Mr Rumsfeld is facing growing criticism from both Democrats and Republicans who are questioning his record in Iraq.

He was given a public grilling from his own troops earlier this month.

During his visit to a US base in Kuwait, American soldiers alleged they had used scrap metal to armour vehicles.

'An insult'

In a statement to the US military newspaper Stars and Stripes, Mr Rumsfeld admitted that in the past he had not personally signed the letters of condolence.

Profile: Donald Rumsfeld

"While I have not individually signed each one, in the interest of ensuring expeditious contact with grieving family members, I have directed that in the future I sign each letter," Mr Rumsfeld's statement said.

"I am deeply grateful for the many letters I have received from the families of those who have been killed in the service of our country, and I recognise and honour their personal loss."

Several families of US soldiers killed overseas said that the machine-signed letters reflected a lack of respect for their losses.

"To me it's an insult, not only as someone who lost a loved one but also as someone who served in Iraq," soldier Ivan Medina - whose twin brother Irving was killed in Iraq last summer - told Stars and Stripes.

The row has led to fresh debates among lawmakers over whether Mr Rumsfeld - whose handling of the invasion of Iraq and its aftermath have come under close scrutiny - should step down.

'Great confidence'

The BBC's Michael Buchanan in Washington says senior Republicans have spent the past few days openly questioning President George W Bush's decision to keep Mr Rumsfeld at the Pentagon.

They claim the defence secretary has to answer for a number of major mistakes made in Iraq, our correspondent adds.

Republican Senator Chuck Hagel, a decorated Vietnam war veteran, told CBS's Face the Nation he had "no confidence" in Mr Rumsfeld.

"This issue of the secretary of defence not personally signing the letters is just astounding to me," he said, noting that President Bush did sign such letters himself.

But President Bush's Chief of Staff, Andrew Card, said Mr Rumsfeld had the full support of the White House.

Mr Card told ABC's This Week that Mr Rumsfeld "is doing a spectacular job, and the president has great confidence in him".

Many leading Republicans have also said he should stay.

Commentary:It took a lot of weeks, but Rumsfeld was finally forced to admit he didn't sign condolence letters. Another day, another lied set to rest. When will this inanity end?