Mr Obama's aide, Ms Valerie Jarrett, fell off a Chicago kerb several weeks ago while her thumbs were flying on her Blackberry. 'I didn't see the sidewalk, and I twisted my ankle,' she said.

Ms Jarrett got off easy.

The American College of Emergency Physicians issued an alert this week warning of the danger of more serious accidents involving oblivious texters.

Emergency room doctors cite rising reports nationwide of injuries involving text-messaging pedestrians, cyclists, in-line skaters and motorists. Most involve scrapes, cuts and sprains from texters who walked into lamp posts or walls or tripped over kerbs.

But doctors say they know of at least two fatal cases in California.

A San Francisco woman was killed by a truck earlier this year when she stepped off a kerb while texting, and a Bakersfield man was killed last year by a car as he was texting while crossing the street.

The United States Consumer Product Safety Commission has no national estimates on how common texting-related injuries are.

But among the reports it has received: A 15-year-old girl fell off her horse while texting, suffering head and back injuries, and a 13-year-old girl suffered burns after texting her boyfriend while cooking noodles.

Dr James Adams, chairman of emergency medicine at Northwestern Memorial Hospital in Chicago, has treated minor texting-related injuries. 'Common sense isn't always common,' he said.

Sometimes, even among doctors. 'I have to admit I started a text while I was driving, and then I said, 'This is so stupid', so I stopped,' he said.

Dr Patrick Walsh, an emergency physician in Bakersfield, California, is a texter, too, but he tries to remind himself to do it intelligently.

'We think we're multi-tasking, but we're not. You're focusing on one task for a split second, then focusing on another one, and with something moving at 64 kmh like a car, it just takes a couple of seconds to be hit.'

Dr Walsh said on a recent visit to Ireland, he noticed a government campaign against texting and walking, aimed at teenagers. The message echoes the US emergency doctors' advice.

'We don't want to sound like some stern schoolmistress, telling people 'don't text on your cellphone'. But when you're texting, look around,' he said.

ASSOCIATED PRESS