Two men on a motorcycle shot and killed an American teacher in the Yemeni city of Taiz, south of the capital Sanaa, on Sunday morning, a local police source said.
A gunman riding on the motorcycle driven by an accomplice shot the man, an English-language teacher and deputy director of a local language school called the Swedish Institute, the source said.
He said the gunmen, who escaped after the attack, were believed to be militants linked to al Qaeda.
Yemen has seen an escalation of violence by the Islamist militant network since President Abd-Rabbu Mansour Hadi took office last month vowing to fight al Qaeda's regional wing.
Yemen's commercial hub of Taiz, located some 200 km (120 miles) south of Sanaa, was a flashpoint for protests against former President Ali Abdullah Saleh's 33 year rule, and where many foreigners in Yemen live and work.