Yemen crisis: Dozens of soldiers killed in air strike
Dozens of soldiers have been killed in a Saudi-led coalition air strike on an army base in southern Yemen.
One military source said the soldiers were loyal to the exiled president and that the facility was hit in error.
But another source claimed the strike was called in to stop the soldiers defecting to the Houthi rebel movement.
More than 3,000 people have been killed since the coalition began an air campaign in March to drive back the rebels and restore the government.
On Tuesday, the UN announced that at least 1,528 civilians were among the dead.
Another one million civilians have been displaced by the conflict and more than 80% of Yemen's 25 million people now need some form of humanitarian aid.
The incident in which the soldiers died reportedly took place on Tuesday night at the headquarters of the 23rd Mechanised Brigade in al-Abr, Hadramawt province, near the border with Saudi Arabia.
A military source told the Spanish news agency Efe that coalition aircraft bombed the base, used by forces loyal to President Abdrabbuh Mansour Hadi, while attempting to stop rebel forces taking control of a nearby border crossing.
The source said that at least 70 soldiers were killed and 200 others wounded.
Efe quoted a statement by army chief Gen Mohammed Ali al-Maqdisi as saying that the strikes had been carried out "in error" and caused fatalities.
However, another military source told the AFP news agency that the coalition had intervened when dozens of soldiers at the base "defected and announced their support" for the Houthis, triggering clashes with pro-government troops.
At least 30 soldiers were killed, and armoured vehicles and troop carriers were destroyed or damaged, before the situation was brought under control, he added.
Two days ago, more than 170 people - most of them civilians - were killed and dozens wounded in coalition air strikes and clashes across Yemen.
The coalition bombardment has so far failed to defeat the rebels and allied army units loyal to ousted former president Ali Abdullah Saleh, who forced President Hadi to flee the country at the end of March as they advanced on Aden.
Mr Hadi had taken refuge in the city the previous month after the Houthis consolidated their control of Sanaa and placed him under effective house arrest.
'Deteriorating by the day'
On Tuesday, the UN High Commissioner for Human Rights expressed deep concern about the situation in Yemen.
Spokeswoman Cecile Pouilly said its team on the ground had been able to document human rights violations, and abuses and violations of international humanitarian law, by all parties to the conflict.
They included abduction, ill-treatment, restrictions on freedom of expression and peaceful assembly, and attacks against humanitarian workers, medical staff and journalists, she added.
Basic public services are also collapsing, with shortages of medicine, essential medical supplies and fuel now at what Ms Pouilly called "critical levels".
Antoine Grand, head of the International Committee of the Red Cross in Yemen, said the situation was "catastrophic in general" and "deteriorating by the day".
The UN also said on Tuesday that it had received only 13% of the $1.6bn (£1bn) needed for its aid operation in Yemen since launching an appeal last month. Saudi Arabia has pledged $274m, but none of the money has yet materialised.