The nonprofit Internet Corporation for Assigned Names and Numbers, or Icann, earlier this year voted to relax the rules on so-called top-level domain names, or TLDs, the suffixes, such as the ubiquitous .com, .net and .org, among others.

Easing the rules could pave the way for companies or individuals to create an array of new addresses for the Web, but the U.S. government said Icann must ensure that introduction of a slew of new names "will not jeopardize the stability and security" of the Internet domain name system.

"It is unclear that the threshold question of whether the potential consumer benefits outweigh the potential costs has been adequately addressed," the U.S. Department of Commerce, said in a letter to Icann dated Dec. 18.

Currently, there are more than 200 TLDs, which also include the two-character country codes used by Web sites, such as Britain's .uk.

Under the proposed system, individuals, companies or groups could apply to have any string of letters established as a domain name. It could be a vanity name, for example -- .smith -- or a category name like .sports or .perfume.

A company could also change its domain to reflect its brand, so Apple.com could become Apple.mac, for instance.

VeriSign Inc now owns the registry for .com and net domain names.

For a company to become such a registry, it would need to apply to Icann, which coordinates the Internet's naming system, at a fee expected to cost more than $100,000.

The U.S. said Icann needs to prove it can handle a potentially huge influx of applications and how it will police issues related to intellectual property rights.

(By Kim Dixon, Editing by Andre Grenon)