At least 60 people have been killed in a suicide car bombing at a military facility in the southern Yemen city of Aden, doctors say.
A training camp, or compound used by the pro-government Popular Resistance militia, was hit, reports say.
So-called Islamic State said it carried out the attack.
It comes amid a fresh push to end Yemen's 17-month-old war between Saudi-backed government and rebels that the UN says has left 6,600 people dead.
Some 2.5 million Yemenis have also been displaced.
IS's self-styled news agency Amaq said the group had carried out Monday's attack.
Meanwhile, the government and rebels have responded positively to a new Gulf-backed initiative to end the conflict.
The plan, announced last week by the US, calls for the withdrawal of Shia Houthi rebels from the capital, Sanaa, and talks on forming a unity government.
The rebels said they were prepared to restart negotiations, provided the Saudi-led coalition stopped attacking and laying siege to territories held by them.
The latest round of peace talks in Kuwait collapsed earlier this month.
The Saudi-led coalition has been carrying out air strikes in Yemen since March 2015 in support of the internationally recognised government of President Abedrabbo Mansour Hadi.
The campaign began after the Houthi rebels, backed by supporters of former President Ali Abdullah Saleh, took over parts of the country, including Sanaa, forcing the government into exile.
The government and its allies have since retaken Aden. Saudi Arabia says the Houthis are supported financially and militarily by its regional rival Iran - something Tehran denies.