A Yemeni Islamist group linked to al Qaeda said on Friday it had attacked and killed a CIA officer in the southern province of Aden, but a Yemeni security official said there were no casualties when a U.S. security team was attacked there.

In a text message sent to journalists in Yemen, Ansar al-Sharia said: The mujihadeen (holy warriors) killed a CIA officer on Thursday while he was in Aden province, after tracking him and determining he was cooperating with the Sanaa government.

An earlier message from the same group said it had targeted a U.S. intelligence officer, without mentioning casualties.

A Yemeni security official in Aden, speaking on condition of anonymity, said a gunman fired on a U.S. security team involved in training Yemeni security forces on Thursday, but that the shots had hit their armoured vehicle without injuring anyone.

(Reporting by Mohammed Mukhashaf; Writing by Joseph Logan; editing by Tim Pearce)