Taxes for Work Done Outside the U.S. by a Foreign Person

[ike]

Hello:

We have several people in Uzbekistan who do some work for us. Work is done entirely outside of the U.S. and these people have not and are not planning to go to the USA for our work-related purposes. Are we liable for any tax in the US associated with these people when we pay them for their services? If so, what tax % are we talking about?
What forms need to be completed?
We are a US business.

Thank you.