Yemeni pro-government fighters gather outside an elderly care home in Yemen's main southern city of Aden after it was attacked by gunmen on March 4, 2016. (AFP Photo)
Yemeni authorities have blamed the ISIS group for an attack on an elderly care home run by missionaries that killed 16 people and was condemned by Pope Francis as "diabolical".
Rival jihadist movement Al-Qaeda distanced itself from the mass shooting in the main southern city of Aden, saying it was not responsible.
Gunmen stormed the refuge operated by Mother Teresa's Missionaries of Charity on Friday, killing a Yemeni guard before tying up and shooting 15 other employees, officials said.
Four foreign nuns working as nurses were among those killed.
Screams of elderly residents echoed from the home during the shooting rampage, witnesses said, recounting seeing the bodies of slain workers with their arms tied behind their backs scattered on the bloodstained floor as the aged residents cried out in fear.
No group has yet claimed the attack in the war-torn country, where the internationally recognised government is grappling with both an Iran-backed rebellion and a growing jihadist presence.
'Treacherous terrorist acts'
An unnamed Yemeni presidency source in Riyadh said that those behind such "treacherous terrorist acts" are individuals who have "sold themselves to the devil," in a statement on the official sabanew.net website.
"There was no trace of these groups, which go under the name of the Islamic State or (its Arabic acronym) Daesh" when pro-government forces were battling the Huthi rebels and their allies to push them out of Aden last year, the source said, accusing them of "switching roles" with the Iran-backed rebels.
In a statement addressed to the residents of Aden, Al-Qaeda in the Arabian Peninsula (AQAP), also known as Ansar al-Sharia, denied "any links to the attack on the elderly care home".
"These are not our operations and this is not our way of fighting," said the group, which has seized parts of southern and eastern Yemen.
Al-Qaeda has previously criticised ISIS for attacks on Shiite mosques in Yemen that left dozens dead.
Al-Qaeda and ISIS have stepped up attacks in Aden, targeting mainly loyalists and members of a Saudi-led coalition battling the rebels since March last year.
The Huthi rebels controlled Aden for months before government loyalists pushed them out in July.
President Abedrabbo Mansour Hadi has declared the city to be Yemen's temporary capital as Sanaa has been in the hands of the Huthi rebels and their allies since September 2014.
But Hadi and many senior officials spend most of their time in Riyadh.
'Senseless and diabolical'
The six-nation Gulf Cooperation Council, which backs the Yemeni government, "strongly" condemned the care home attack which it said "reveals the goals of forces which are against the return of security and stability to Yemen".
The Vatican's Secretary of State Pietro Parolin meanwhile said that "his Holiness Pope Francis was shocked and profoundly saddened to learn of the killing of four Missionaries of Charity (nuns) and 12 others at a home for the elderly in Aden."
"He sends the assurance of his prayers for the dead and his spiritual closeness to their families and to all affected from this act of senseless and diabolical violence," Cardinal Parolin said in a statement.
Friday's shooting was not the first deady attack on the Mother Teresa order in Yemen.
In 1998, three of its nuns were shot dead in western Yemen by a psychiatric patient who had volunteered to fight alongside Bosnian Muslims in 1992 before returning to the Arabian Peninsula country.
In December, suspected jihadists blew up a small deserted Catholic church in Aden dating from the 1950s when the city was a British protectorate.
Months earlier in September, masked arsonists had torched the Saint Joseph Catholic church in the central Crater neighbourhood of Aden.
Of the 22 churches that operated in Aden when the city was a British colony before 1967, only a few remain open, used rarely by foreign workers and African refugees.