A church has been blown up in the latest tragedy to take place during the calamitous conflict in Yemen.

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

Around 6,000 people have already died in the six-month-old war which is being fought between Iranian backed Houthi fighters and a coalition headed by Saudi Arabia.

Oxfam has described the situation in Yemen as, "The world's largest forgotten emergency."

"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 said.

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.

Islamist militants carry out frequent attacks, and have seized government buildings and occasionally deploy on the streets unhindered. Meanwhile 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.

Christian Today has previously reported on British and American complicity in the war. Oxfam has asked serious questions about why the West is still supplying Saudi Arabia with arms, despite evidence of huge suffering in Yemen. A spokesperson said, "Between January and March this year, the UK approved two orders for bombs or missiles for Saudi Arabia, valued at £17.19m... Since then, the Ministry of Defence has told Parliament that the UK has continued to supply 'precision guided weapons' to Saudi Arabia under its existing arrangements... The government has also confirmed that the UK is continuing its support and maintenance for UK-supplied equipment, with MoD military and civilian personnel, as well as BAE Systems personnel stationed in Saudi Arabia to support the Royal Saudi Air Force."

Additional reporting by Reuters.