Apple was today monitoring the latest mini-crisis to hit its much-hyped iPhone after some users began reporting that the touchscreen did not work.

Threads on several Apple forums – including the company's own – have been devoted to the problem, which causes parts of the device's screen to go 'dead' and stop responding to the touch of a finger.

Typically the dead spot is a strip about half an inch wide that runs the width of the iPhone's screen as it is held vertically, users experiencing the problem said.

In one case, the strip ran across the Unlock button, which meant that the user was unable to answer the phone when it rang.

"On the main screen, I can't hit the button for clock, calculator, notes of settings," 'Gwas', a user of the Apple-dedicated site Mac Rumors, wrote. "For text messages, I can't hit the send button. On the phone keypad I can't hit the 7, 8, or 9 keys."

Another complainant wrote: "Now like 1/4 of the screen – starting from the bottom – doesn't work."

The problem, which was first reported two weeks ago, cannot be fixed by running any of the updates Apple has issued for the device, nor by resetting the phone, affected users said.

Some whose screens were broken reported that Apple had been willing to replace the device, but others complained that the company had demanded a fee for loaning them an iPhone while theirs was being repaired.

"They refused to give me a replacement phone and would not waive the $29 fee for a loaner," 'Tjrub' wrote on the Apple Insider site.

Threads given over to the 'dead spots' on Apple's own site had been deleted, one user said, suggesting that the company had recognised the problem was widespread.

Times Online found one touchscreen-related post on the Apple site, submitted early this morning, which said: "The bottom of my touchscreen is completely dead – only a few inches work. Can anyone help me?"

Apple has so far not made any statement on the issue, and was not immediately available for comment today.

The touchscreen issue is the latest in a series of complaints that have been made about the iPhone. Others have suggested that the device's AC adapter is unreliable and that the device's security is weak. One owner is also suing Apple alleging that the company misled customers about how long the battery would last before needing to be replaced.

Explore Personal Tech

• InGear