GARDEZ, Afghanistan -- Mercenaries from as far as Siberia are strengthening the ranks of the Taliban in Afghanistan, The New York Times reported Tuesday.

Several hundred foreign fighters have been recruited to Afghanistan this year in the largest influx since 2001, the Times reported.

The mercenaries are from Pakistan, Uzbekistan, Siberia, several Arab countries and perhaps Turkey and western China, U.S. military officials told the Times, noting the foreign fighters are more uncontrollable and extreme than Taliban militants from Afghanistan.

The foreign fighters are transforming the Taliban into a loose network that includes drug traffickers and Afghans tired of Western intervention in their country, the Times reported.

"They play an incredibly important part in the insurgency. They act as a force multiplier in improving their ability to kill Afghan and NATO forces," said Seth Jones, a Rand Corp. analyst who called the arrival of the foreign fighters a dangerous development.