partnership has no US source income? All operations are conducted outside of the US?

Probably more question to ask your client...  I'd probably ask my client what the purpose of setting up a US partnership is and how the transactions are structured before drawing a conclusion.

By virtue of setting up a US partnership, your client has a US office/fixed place of business for domestic tax and treaty purposes.  This is an important consideration for purposes of determining whether there is any ECI pursuant to §1.1446-2, even if the operations are conducted outside the US, especially with respect to §864.