NIC Query

A client has set up a UK company with a view to supplying specialist staff to Middle Eastern countries.  The initial tranche of specialists being supplied are all from the USA, they pay US tax and are normally US resident.  They will at no time be resident in the UK or have any duties arising in the UK.  All duties will be carried out in the Middle East. 

Is there a legal obligation to operate a PAYE scheme for the company and will there be employer's or employees' national insurance arising on the salaries paid to these US specialists?  It is fairly clear that no UK tax liability arises on the remuneration. Thanks in advance for any advice readers can give!