The United States is the only force known to operate armed drones over Yemen.
"A drone likely to be American" killed all seven overnight as they were aboard three vehicles on the road from the southern province of Shabwa to the central province of Bayda, the official said.
Washington considers the Yemen-based Al-Qaeda in the Arabian Peninsula to be the radical group's most dangerous branch.
A long-running drone war against AQAP has intensified since US President Donald Trump took office in January.
AQAP has flourished in the chaos of the country's civil war, which pits the Saudi-backed government against the Huthi rebels.
More than 8,700 people have been killed in the conflict since a Saudi-led military coalition intervened on the government's side in March 2015.
Al-Qaeda's jihadist rivals, the Islamic State group, have also carried out several deadly attacks in the country.
Last month, the United States said it had killed dozens of IS fighters at training camps in Bayda.