SANAA, Yemen (AP) -- A suicide bomber on Sunday detonated his explosives among policemen standing in line outside a police base in the southern Yemeni city of Mukalla, killing 25, security and health officials said. At least 17 more people were injured in the attack and the officials said the death toll was likely to rise further.
The Yemeni affiliate of the extremist Islamist State group claimed responsibility for the attack in a statement posted on social media networks by IS sympathizers.
Sunday's victims were policemen returning to work for the first time since last month's recapture of Mukalla by forces loyal to the internationally-recognized government. The port city had been held for more than a year by Yemen's local al-Qaida affiliate.
The victims also included young men applying for jobs with the city's local police, according to the officials, who spoke on condition of anonymity because they were not authorized to speak to the media.
The IS group has been trying to gain a foothold in Yemen, where a war pitting the country's Shiite rebels, known as Houthis, against President Abed Rabbo Mansour's government, which is backed by a Saudi-led coalition, has left a security vacuum throughout parts of the country.
The U.N. special envoy to Yemen said Sunday that the warring parties agreed to an exchange of 50 percent of prisoners and detainees held by both sides before the start of the Muslim holy month of Ramadan, which is expected to start around June 6. Ismail Ould Cheikh Ahmed did not give a number for how many prisoners this deal would free.
He was speaking to reporters in Kuwait, which is hosting U.N.-brokered negotiations to resolve the conflict. A truce, which began April 10, has mostly held despite multiple breaches by both sides. The U.N. envoy acknowledged in a statement late Saturday that the talks are showing progress "albeit at a relatively slow pace."
Sunday's blast came a week after the IS in Yemen claimed responsibility for an explosion that struck a navy base in Mukalla, killing at least six soldiers.
The IS affiliate in Yemen emerged during the country's ongoing civil war and has been striving to expand its footprint amid the turmoil gripping the impoverished country in the southern corner of the Arabian peninsula.
Throughout its year-long rule of Mukalla, al-Qaida forged an alliance with local forces fighting the Houthis in cities like Taiz and Aden. Those local fighters are backed by the Saudi-led coalition, a reflection of the complexities of Yemen's conflict.