Unknown gunmen killed a prominent politician in Yemen's southwestern province of Taiz on Wednesday, a local security official said.

The assassination took place in the port city of Mocha, located in the western part of Taiz, where Al-Haisi, a leading member of the Muslim Brotherhood-affiliated Islah party, was ambushed by masked gunmen armed with assault rifles, the official said on condition of anonymity.

The assailants opened fire on Al-Haisi's vehicle, killing him instantly, the official added.

The attackers managed to escape after the drive-by shooting, the official said, adding local security forces have launched an investigation into the murder.

In a statement, the Islah party confirmed Al-Haisi's death and said he was "one of the pioneering leaders of the popular resistance on the Taiz fronts who had actively participated in military operations against the Houthi rebels during the previous years."

So far, no group has claimed responsibility for the assassination.

Yemen has been embroiled in a civil war since late 2014, when the Houthi rebel militia attacked several northern cities and forced the internationally-recognized Yemeni government to leave the Yemeni capital of Sanaa.