Two masked gunmen riding a motorcycle opened fire and killed a photojournalist in Yemen's southern port city of Aden on Tuesday.

The freelance photojournalist, identified as Nabil Hassan, was killed by assualt rifles of the gunmen "while he was getting out of his house in Aden," the official said on condition of anonymity.

The assailants fled the scene immediately after firing two bullets toward Hassan's head and heart in his residential neighborhood on the northern outskirts of Aden, according to source.

A number of security units were deployed to search for the perpetrators in Aden's district of Dar Sad, he added.

Yemeni Minister of Human Rights Mohammed Askar strongly condemned the killing of Hassan, demanding the security forces immediately capture the perpetrators.

"The assassination ... is a new attempt to silence the right to freedom of expression and revealing the truth. I urge the authorities to take responsibility for capturing the perpetrators and bringing them to justice," Askar said in a brief press statement.

Yemen has been locked into a civil war since the Iran-backed Shiite Houthi rebels overran much of the country and seized all northern provinces, including the capital Sanaa, in 2014.

Saudi Arabia has been leading an Arab military coalition in Yemen since 2015 to support the government of President Abd-Rabbu Mansour Hadi after Houthi rebels forced him into exile.