By Katie Marsal

Published: 06:50 PM EST

Checks with stores across the US show Apple to have been virtually devoid of iPhone stock for days, even at its online store -- and with signs that the company is aware of its widespread nature.

When AppleInsider contacted stores across the country, the answer was always the same: all stock of 8GB and 16GB iPhone models was completely sold out, and clerks were unsure of when their stores were receive more.

This included flagship outlets in Chicago, New York City, and San Francisco.

Staffers at some stores also appear to have been briefed ahead of time that other stores besides their own were also completely without supplies of the Apple handset. When contacting the Fifth Avenue store, the clerk noted that "all three New York stores" were without stock. At Miami's store at The Falls, one employee stated that supplies were "constrained" throughout all of Florida as well as in New York.

The sudden shortfall has been further confirmed by reports from AppleInsider readers. In several cases, their own investigations reported all stores in a given state running out, including Michigan, New Jersey, Pennsylvania, and Texas. Many if not all AT&T stores were also said to have run out of inventory.

Apple's online store for the US, usually a bellwether of overall supply, currently shows a 5-7 day shipping delay for iPhones regardless of model.

The latest check reveals a shortage that has only been exacerbated since it began last week on a smaller scale. International stores have fared better, though Apple France continued to show only the 8GB model as available. Austrian, Irish, and German stores list both models, though none of these currently allow customers to order the iPhone online.

Despite the pervasive issue, Apple has not provided an official explanation for its rapidly depleting iPhone offerings. The shortfall comes months ahead of new models predicted by analysts and is uncharacteristic for the modern incarnation of the Cupertino, Calif.-based electronics firm, which quickly recovered its inventories even from the initial iPhone shortage that followed the weekend after the product's launch in June 2007.

When pressed, one retail clerk in Las Vegas' Fashion Show Apple store would only venture that there was likely a mismatch between supply and demand.

"They're just popular," the worker said.