UK-born US journalist Luke Somers and South African teacher Pierre Korkie have been killed by al-Qaeda militants in Yemen during a failed rescue bid.
Saturday’s operation was carried out by joint US and Yemeni special forces in the southern Shabwa region.
US President Barack Obama condemned Mr Somers’s death as a “barbaric murder”.
They were being held by militants from al-Qaeda in the Arabian Peninsula (AQAP), regarded by the US as one of the deadliest offshoots of al-Qaeda.
The group is based in eastern Yemen and has built up support amid the unrest which has beset the impoverished country since the overthrow of President Ali Abdullah Saleh in 2011.
Analysis: Frank Gardner, BBC Security correspondent
Luke Somers is believed to have been sold on by his abductors to AQAP, described as the most dangerous of all al-Qaeda’s regional affiliates.
The group has earned itself millions of dollars by ransoming hostages but the US and British governments refuse to pay, leaving them little room for negotiation.
Experts believe the group may now be looking to compete with Islamic State, in Syria and Iraq, which has gained worldwide notoriety for its extreme violence and cruelty coupled with highly produced videos uploaded on to the internet.
President Obama said he authorised the raid to rescue Mr Somers and other hostages held in the same location.
He said information had “indicated that Luke’s life was in imminent danger”.
A number of militants were also killed in the operation.
“Terrorists who seek to harm our citizens will feel the long arm of American justice,” Mr Obama said.
However, a charity working with Mr Korkie said that they had expected his release on Sunday, and that the US rescue attempt had “destroyed everything”.