DUBAI (Reuters) - Four people were killed and several others injured on Sunday when a suicide car bomb exploded outside the home of the director of security for the southern Yemeni port city of Aden, eyewitnesses and medics said.

The four men killed were guards for Brigadier General Shalal Ali Shayyeh, who survived a car bomb attack on his convoy on Jan. 4 amid an escalating wave of assassinations against security forces in the city.

The government of President Abd-Rabbu Mansour Hadi has been grappling with lawlessness there since militiamen, backed by a Saudi-led Arab military alliance, drove the Iran-allied Houthi group out in July.

Yemen descended into a civil war last March when the Houthis forced Hadi to flee to Saudi Arabia after they closed in on Aden, drawing a Saudi-led coalition into the Yemen conflict.

Alliance and anti-Houthi forced seized Aden from the Houthis over the summer but have yet to impose control on the city where militants and other gunmen have a prominent presence.

In a rare security incident in the Houthi-controlled capital Sanaa, gunmen on a motorbike also shot dead a police colonel.

Ground fighting and air strikes have killed around 6,000 people during the nine-month war in impoverished Yemen. The United Nations estimates about half that number are civilians.

A local official in the village of Bilad al-Rus outside Sanaa said a prominent local journalist, Almigdad Mojalli, was killed in a Saudi-led air strike on Sunday.

Mojalli, a reporter for several Western and international news outlets, died while investigating the site of a mineral bath that residents said was hit by coalition planes last week, killing 15 civilians.