On Sunday, two men disguised as Yemeni soldiers shot and killed Joel Wesley, an American teacher who worked at a language institute in Taiz, as he sat in his car, according to the reports.
Taiz is the second largest city in Yemen and was a center of the anti-government protests that ultimately ousted longtime Yemeni leader Ali Abdullah Saleh from power in February.
The attack was carried out by Ansar al-Shariah, a jihadist group tied to al Qaeda branch in Yemen known as Al Qaeda in the Arabian Peninsula (AQAP), according to the Journal.
The terror cell branded Wesley, who arrived in Yemen in 2010, an "enemy of Islam" for preaching Christianity to locals during his tenure at the institute, the report states.
The incident also comes days after Yemeni officials agreed to let U.S. special operations units come back to the country and resume counterterrorism training operations with local forces. Current president President Abdu Rabu Mansour Hadi signed off on the deal in early March.
U.S-led training operations had been on hold since last year, as Yemen became one of many countries caught up in the "Arab spring" uprisings that swept across the Middle East.
Pentagon and intelligence officials have recognized al Qaeda's Yemen cell as one of the group's most active and dangerous. AQAP leaders were behind a failed 2009 plot to blow up an American airliner above Detroit and a 2010 attempt to set off a car bomb in the middle of Times Square in New York City.
Former AQAP leader Anwar al Awlaki is believed to have spurred on Nidal Malik Hassan to kill 13 U.S. soldiers during a shooting spree at the Army's base in Ft. Hood, Texas. The American-born Awlaki was killed in an air strike by a U.S.unmanned drone last September.
It was the first time the White House approved the targeting and killing of a U.S citizen in a counterterrorism operation.