The pro-government army commander of Yemen's Aden survived a car bombing in the second city on Thursday that left one of his bodyguards dead, a military official told AFP.

General Ahmed Saif al-Yafie, commander of the Fourth Military Region, which includes Aden and its surroundings, escaped unharmed when an explosive device planted in his vehicle blew up, killing the guard, the source said.

There was no immediate claim of responsibility for the attack.

Aden, declared by the government as Yemen's temporary capital, has been the scene of growing unrest as Al-Qaeda in the Arabian Peninsula, long active in Yemen, and the newly emerged Islamic State group appear to be vying for influence in the port city.

It was rocked by months of fighting this year between pro-government forces and Iran-backed rebels who seized the capital Sanaa in September 2014 before expanding south.

Supported by a Saudi-led coalition, loyalists have regained control of Aden and four nearby provinces in the south since July as fierce battles persist across the country.

In another sign of increasing insecurity, unknown gunmen shot dead a leading member of the pro-government Popular Resistance militia and two of his bodyguards, security officials said.

They were killed in a drive-by shooting in central Aden overnight Wednesday and the gunmen fled after the attack, the sources said.

The government has been struggling to exert control over Aden as jihadist groups exploit the conflict to make sweeping gains, particularly in southern regions.

The extremists are occupying government buildings and are frequently seen patrolling several districts of Aden.

They have carried out several deadly attacks, assassinated government officials, and intimidated civilians.

On Thursday, radical Islamist gunmen shut down the faculty of engineering at the University of Aden for the second time this week and kidnapped its dean, students said.

The gunmen, who arrived aboard four military vehicles, forced the gates shut to protest against mixing of the sexes on campus, students said.

"No mixing. We had previously warned the university," the students quoted the gunmen as saying.

The university said it has suspended all classes and closed all its faculties until further notice.

On Tuesday, gunmen locked down the faculties of administrative sciences, law, and engineering in an attempt to force male and female students to keep apart on campus.

Witnesses and residents say the radical gunmen are loyalists of Ayman Askar, a local militia leader known for his links to both Al-Qaeda and IS.

Last month, gunmen shut the faculty of administrative sciences and threatened to use force against students if they did not observe segregation of the sexes.

Early in December, IS claimed the killing of Aden's newly appointed governor in a bombing.

Jaafar Saad was replaced by the leader of the Popular Resistance in the southern Daleh province, Aidarus al-Zubaidi.

Zubaidi's deputy, General Shallal Ali Shayae, was named Aden's police chief as authorities deployed some 500 fighters across the city, according to security sources.