Kidnapped Red Cross doctor Khalil Rasjed Dale was found with his throat slit in south-west Pakistan on Sunday.
Dr Dale was managing a health programme in Quetta in January when he was snatched from the streets by armed men.
A note attached to his body said he had been killed because no ransom was paid.
The identity of his killers is not known, but Baluchistan province where he worked has seen violence involving both separatists and Islamist fighters.
The International Committee of the Red Cross condemned Dr Dale's killing as a "barbaric act.
"All of us at the ICRC and at the British Red Cross share the grief and outrage of Khalil's family and friends," said director-general Yves Daccord.
A drone strike killed two people in North Waziristan described as "suspected Islamists" by US intelligence officials.
The latest attack came as Washington attempts to coax Islamabad to reopen supply lines to Afghanistan that it closed in November following a US drone strike that killed 24 Pakistani soldiers.
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Attacks such as yesterday's horrific murder in Woolwich didn't happen before the 'war on terror.' It's time we recognised the consequences of the conflicts we've unleashed