A Yemeni militant group affiliated with al-Qaida says it has shot and killed an American teacher in southern Yemen for preaching Christianity.

Militants riding a motorcycle shot the man in his car in the southern city of Taiz on Sunday. Yemeni officials say the American had been working at a European-run language institute. Authorities launched an investigation to find the perpetrators of the attack.

A U.S. State Department official confirmed the killing of the U.S. citizen in a statement sent to VOA, condemning it as a “heinous crime” and urging Yemen to bring those responsible to justice.

Al-Qaida linked group Ansar al-Sharia sent a text message to Yemen-based journalists saying it killed the American because he was a Christian missionary. Islamist militants often accuse Western aid and development groups of proselytizing.

A Swiss woman working as a language teacher in Yemen's western port of Hodeida was abducted last week. The identity of the kidnappers remains unclear.

Al-Qaida's Yemeni affiliate is active in Yemen's center and south, where its fighters seized several towns in Abyan province last year.

A local official told foreign news agencies that missiles fired from the sea struck al-Qaida positions north of Abyan's provincial capital, Zinjibar, beginning Saturday. The official said at least 14 militants were killed. It was not clear if Yemeni or U.S. warships fired the missiles.

Witnesses said Yemeni government warplanes also attacked the al-Qaida-held town of Jaar on Sunday, prompting residents to flee their homes. There were no immediate reports of civilian casualties.

Yemen has been in chaos since last year when anti-government protests forced longtime autocratic ruler Ali Abdullah Saleh to agree to resign as president. His deputy Abed Rabbo Mansour Hadi took over as president last month, vowing to fight al-Qaida and stabilize the impoverished nation.