Al-Qaeda militants killed at least 20 Yemeni soldiers on Saturday when they ambushed their convoy in the south of the war-torn country, a military source said.
Al-Qaeda swiftly denied it was behind the killings.
"Armed members of Al-Qaeda ambushed a group of young soldiers travelling in three civilian vehicles in the province of Abyan, killing at least 20 of them," said the source, who requested anonymity.
The assailants ordered the soldiers to get out of the vehicles and gunned them down early in the morning in the town of Ahwar, the source told AFP.
The soldiers were young recruits who were being deployed as part of the internationally recognised government's efforts to restore security to areas under its control.
They had been travelling to a military camp in Hadramawt, the neighbouring province whose capital has been held by Al-Qaeda since April last year.
Al-Qaeda in the Arabian Peninsula (AQAP), also known as Ansar al-Sharia, in an online statement denied it was involved in the attack.
"We in Ansar al-Sharia deny any connection to the murder incident that took place on Saturday morning in the Ahwar area," it said, blaming a local tribal leader for the killings instead.
Yemen has been at war since September 2014, when Iran-backed Shiite Huthi rebels and their allies drove the government out of Sanaa and much of the country's north.
The Huthis controlled Aden, the main city in southern Yemen, for months before government forces backed by a Saudi-led military coalition pushed them back in July.
Jihadists of AQAP and the Islamic State group have taken advantage of the chaos to strengthen their grip on southern Yemen.
But after having long ignored them, forces loyal to President Abedrabbo Mansour Hadi have launched operations against them in the past few weeks.
- Doubts over ceasefire -
Jihadist attacks on symbols of the state have increased in southern Yemen, in an apparent attempt to hamper the government's efforts to rebuild the army and security forces.
In mid-February, a suicide bomb attack claimed by IS reportedly killed at least 14 soldiers at a military camp in Aden, where young recruits had been undergoing training.
Elsewhere on Saturday, loyalist forces clashed with Shiite Huthi fighters in Marib province for a second consecutive day, according to military sources.
The clashes in the Sarwah region have so far killed 21 people, 13 of them loyalists and eight rebel fighters, the sources said.
The Saudi-led coalition carried out two air strikes to stop the advance of Huthis seeking to take back a military base that pro-government forces had recaptured in late 2015.
The developments come before a UN-announced ceasefire that is due to take effect on Sunday night, ahead of peace talks that are scheduled to be held in Kuwait on April 18.
One loyalist fighter, Ahmed al-Shalafi, said he doubted the rebels would respect the truce.
"How will they observe a ceasefire while they continue to attack us," he said, adding that the two sides had sent in reinforcements to the front line in Sarwah.
Meanwhile, in the region of Nahm, northeast of Sanaa, clashes on Saturday killed three loyalists and four rebel fighters, said another military source.
The United Nations says the violence in Yemen has killed nearly 6,300 people since March last year -- half of them civilians.
