ADEN - Gunmen attacked a care home run by missionaries in Yemen's jihadist-plagued southern city of Aden on Friday, killing 16 workers including four foreign nuns, officials said.

There was no immediate claim of responsibility, but Aden has seen a surge in attacks by the Islamic State group and rival Al-Qaeda. Four gunmen entered the refuge operated by Mother Teresa's Missionaries of Charity in Aden's Sheikh Othman district, killing a guard before tying up and shooting employees, security officials told AFP.

Screams of elderly residents echoed from the home during the shooting rampage, witnesses said. They recounted 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. The four foreign nuns killed were identified as two Rwandans, a Kenyan and an Indian, according to the Vatican missionary news agency Fides, which said the mother superior managed to hide and survive.

Apart from the foreigners, the rest of those killed were Yemenis working at the facility, officials said. In addition, an Indian priest was missing, Fides said, citing Bishop Paul Hinder, the apostolic vicar of southern Arabia. The assailants tied up their victims in different parts of the building before opening fire on them, said a security source cited by the official website.

"We have never witnessed such a brutal crime," he said, adding that the killing spree lasted for one hour. "I went out for Friday prayers. When I came back, I found all my friends dead," one resident said. It 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. The latest attack comes with Yemen's internationally recognised government grappling with an Iran-backed rebellion on one side and a growing jihadist presence on the other. Prime Minister Khalid Bahah said security forces were hunting down the "terrorists" who carried out the attack. One official said the attackers were "extremists" and blamed the Islamic State group, which has been gaining ground in Aden in recent months.

President Abedrabbo Mansour Hadi has declared Aden to be Yemen's temporary capital as Sanaa remains in the hands of the Huthi rebels and their allies since they seized it in September 2014. Further east, a suspected drone strike hit a vehicle carrying Al-Qaeda militants in Shabwa province, killing four, government and tribal sources said Friday. Only the United States is known to operate armed drones over Yemen.

Al-Qaeda and IS have stepped up attacks in Aden despite the efforts of the government and its backers in a Saudi-led coalition battling the Huthis to secure it. However, most attacks have so far targeted coalition forces and pro-government Yemeni troops. Late on Thursday, gunmen in the city killed Hussein al-Wuhayshi, a leader of a pro-government militia formed in the south in 2011 to fight Al-Qaeda, along with his brother, a security official said.

On Monday, a suicide car bombing in Sheikh Othman hit a gathering of loyalist forces, killing four people and wounding five others, according to a security official. The Huthi rebels controlled Yemen's main port city for months before government loyalists pushed them out in July. Because of the unrest gripping Aden, Hadi and many senior officials in his government spend most of their time in Riyadh. Al-Qaeda has been well-established for years in south Yemen, but now faces competition from IS which has mounted a series of deadly attacks, particularly in Aden.

In December, suspected jihadists blew up a small deserted Catholic church in the city dating from the 1950s when Aden was a British protectorate. The UN says more than 6,000 people have been killed in the Yemeni conflict with over 80 percent of the population in dire need of food, medicine or other basic necessities.

RUSSIA WARNS OF 'VERY LONG' WAR IN YEMEN: Russia warned Thursday the war in Yemen could grind on for a "very long time" because of the government's insistence on conditions for a ceasefire.

Russian Ambassador Vitaly Churkin, speaking to reporters after a UN Security Council meeting on the Yemen crisis, told reporters he was concerned that prospects for peace talks were dim.

"We hear that the government does not want to have a ceasefire until there is a comprehensive settlement," Churkin said. "This is a recipe for a very long conflict which will have even more dramatic results," he said. Russia has repeatedly criticized the Saudi-led bombing campaign in Yemen that was launched last March to push back Iranian-backed Huthi rebels.

More than 6,000 people have been killed in the conflict. It has brought the country to its knees, with more than 80 percent of the population in dire need of food, medicine or other basic necessities.

Russia abstained, but did not veto, a Saudi-backed resolution adopted last year that demands that the Huthi rebels withdraw from all territory seized in their campaign.

That resolution, Churkin said, "is being used essentially to continue the military campaign" by the Saudi-led coalition.

UN envoy Ismail Ould Cheikh Ahmed last month told the council that he was hoping to convene peace talks this month to follow up on a first round of consultations held in Switzerland in January.

But the envoy did not announce a date for new talks during his closed-door briefing to the council, diplomats said.

Yemen's Ambassador Khaled Alyemany said his government was ready to take part in talks but accused the rebels of failing to fulfill their commitment to release detainees among other confidence-building measures.

Alyemany accused the Huthis of blocking aid convoys and looting relief supplies that he said were being sold on the black market.