A suicide bomber has killed at least 25 police recruits inside a compound in the southern Yemeni city of Mukalla, according to medical and security sources.
The victims were queuing up in the Fowa compound when the bomb went off. Extreme Islamist group Isis claimed responsibility for the attack, in which about 25 others were wounded.
It was the second deadly blast in four days to hit the city, a hub for rival Islamist group al-Qaeda before it was pushed out last month in an offensive by Yemeni troops backed by a Saudi-led coalition.
The police officers were returning to work for the first time since last month's recapture of Mukalla by the Government's forces.
The Yemeni affiliate of Isis claimed responsibility for the attack, saying the attacker was a "martyrdom-seeker" who had detonated his explosive belt.
The city's security director, Mubarak al-Awthaban, who was at a nearby office when the suicide bomber struck, survived, security sources said.
Before being forced out, al-Qaeda militants took advantage of more than a year of war between the Iran-allied Houthis and supporters of the Saudi-backed President Abd-Rabbu Mansour Hadi to carve out a mini-state stretching across much of the southern coast, including Mukalla.
Their militant rivals in Yemen's branch of Isis, also known as Islamic State or Daesh, have carried out a series of suicide attacks on all sides in Yemen's tangled conflict.
The growing Islamist militant threat has led the Houthis and the Yemeni government to embark on peace talks now under way in Kuwait.
Saudi Arabia, the UAE and other Arab countries intervened in the war in March 2015 in support of the government, which had been swept into exile by the Houthis.
Al-Qaeda in the Arabian Peninsula (AQAP) and Isis view the Arab coalition as a pawn of the West and see the Shia Muslim Houthis as apostates.
The US military announced last week it had deployed a small number of personnel to Yemen to aid in the fight against AQAP, its first troop presence in the country since the Houthis took much of the country.
The Associated Press and Reuters contributed to this report
