XPATH not working ns2:namespace preifix not defined error

Hi am trying to extract the value of UniqueID using the xpath /ns0:Start/ns0:Area/ns0:Test/ns0:Identifier/ns2:UniqueID but its not working pls help me i need normal xpath as well as an MEL command

<?xml version="1.0" encoding="UTF-8"?>
<ns0:Start xmlns:ns0="http://ift.tt/1HMDtM3">
  <ns0:Area>
    <ns0:Test>
      <ns0:Identifier>
        <ns2:UniqueID xmlns:ns2="http://ift.tt/1xECgDH">123456</ns2:UniqueID>
      </ns0:Identifier>
    </ns0:Test>
    <ns0:Test>
      <ns0:Identifier>
        <ns2:ExternalOrderID xmlns:ns2="http://ift.tt/1xECgDH">external</ns2:ExternalOrderID>
      </ns0:Identifier>
      <ns0:Info>
        <ns0:Status>st</ns0:Status>
      </ns0:Info>
    </ns0:Test>
  </ns0:Area>
</ns0:Start>