A suicide car bombing claimed by the Islamic State group in Yemen's southern city of Aden on Monday killed at least 45 pro-government recruits, officials said.

The men were at a staging area near two schools and a mosque when a pickup truck suddenly accelerated through the building's gate as a food delivery arrived, exploding amid the crowd, witnesses said.

"Bodies and body parts are scattered all over the place," said Mohammed Osman, a neighbor who rushed to the scene. "It was a massacre," he said.

Over 60 wounded were being taken to three area hospitals, Yemeni security officials said, speaking on condition of anonymity because they were not authorized to speak to the media. They identified the bomber as one Ahmed Seif, distributing a photo of him smiling and holding an assault rifle next to a flag used by Islamic extremists as well as a rocket grenade launcher.

Yemen is embroiled in a civil war pitting the internationally recognized government and a Saudi-led coalition against the Shiite Houthi rebels, who are allied with army units loyal to a former president. The fighting has allowed al-Qaida and an IS affiliate to expand their reach, particularly in the south.

The recruits were signing up to join a new unit the Saudis hope will ultimately be made up of 5,000 fighters. After some training, the new force will deploy to the Saudi cities of Najran and Jizan, near the border with Yemen, the officials said. The Houthis control most of northern Yemen, including the border regions and the capital, Sanaa.

Aid group Doctors Without Borders reported on social media that their hospital in Aden had received 45 dead, while the Yemeni officials earlier put the figure at 25 but said it was likely to rise.

The IS-run Aamaq news agency said the attack was carried out "by a fighter from the Islamic State who targeted a recruitment center."

Ahmed al-Fatih, who had been working at the center, said security at the site was lax.

"There was no consideration of security," he said. "So it was easy for al-Qaida or Daesh to pull off such an act," he added, using an Arabic acronym to refer to IS.

The U.N. and rights groups estimate at least 9,000 people have been killed since fighting escalated in March 2015 with the start of Saudi-led airstrikes targeting the Houthis and their allies. Some 3 million people have been displaced inside the country, the Arab world's poorest.

U.N.-mediated peace talks in Kuwait were suspended earlier this month with no signs of progress.

The Houthis and forces allied to former President Ali Abdullah Saleh seized Yemen's capital, Sanaa, in September 2014, forcing the internationally recognized government to flee the country. The Saudi-led campaign against the Houthis has pushed them out of southern Yemen, but has failed to dislodge them from Sanaa and the rest of the north.