Unknown attackers blew up an abandoned Catholic Church in the southern Yemeni port city of Aden on Wednesday, residents said, days after Islamic State militants assassinated the city's governor.

Yemen's embattled government is based in Aden but has struggled to impose its authority there since its forces, backed by Gulf Arab troops, expelled the Iran-allied Houthi fighters, who control the capital Sanaa.

Islamist militants carry out frequent attacks, and have seized government buildings and occasionally deploy on the streets unhindered. Nearly 6,000 people have died since Yemen's civil war sparked a Saudi-led military intervention in March.

"The gunmen, who were probably extremists, blew up the Catholic church in the Mualla district of Aden," one resident told Reuters. "We heard a strong explosion which sent a big plume of smoke into the air and afterward saw that the building was completely destroyed," he added.

The Immaculate Conception Church built during the British colonial era in the 1960s was already severely damaged after a Saudi-led coalition air strike in May, a statement from the Catholic Church at the time said.

The Houthi group says it led a revolution against the corrupt government of President Abd-Rabbu Mansour Hadi, but his administration and Gulf allies say they carried out a coup and are advancing Iranian influence in the Arab world.

Once a cosmopolitan city home to thriving Hindu and Christian communities, Aden has gone from one of the world's busiest ports as a key hub of the British empire to a largely lawless backwater.

Its small Christian population left long ago. Unknown assailants had previously vandalised a Christian cemetery and torched another Aden church this year.

Islamic State claimed responsibility for a car bomb which killed governor Jaafar Mohammed Saad on Sunday.

His replacement, Aidarus al-Zubaidi, pledged on Friday to "cleanse Aden of the partisans of chaos."

"We won't allow chaos and a security vacuum which allows these elements to commit their crimes to continue in Aden," al-Zubaidi said in a statement broadcast of state TV.