text: The so-called Islamic State group (IS) has said it carried out the attacks.
  The group has established a presence in Yemen since a civil war broke out there and has carried out numerous attacks.
  It is opposed to the government and Shia Houthi rebels who have seized much of the country, including the capital Sanaa.
  The attacks come on the eve of the first anniversary of the Saudi Arabia-led coalition against the rebels.
  Both civilians and military personnel were killed by the blasts, officials said. Dozens of others were wounded.
  Two of the bombings hit checkpoints next to a base used by the coalition, they said. Gunmen then tried to attack the place.
  The third explosion happened when an ambulance laden with explosives was detonated next to a military checkpoint.
  No end in sight to war in Yemen
  Practising medicine under fire in Yemen
  The war the world forgot?
  Yemen's humanitarian catastrophe
  Who is fighting whom?
  Meeting the Houthis and their enemies
  Aden was recaptured by government troops backed by the Saudi-led coalition last year.
  The campaign was launched in March 2015 in an attempt to oust the rebels from Sanaa and restore Yemen's government.
  Riyadh says the Houthis, who are allied with forces linked to the former president, are supported militarily by its regional rival Iran, something it denies.
  Since the offensive started, more than 6,200 people have been killed, half of them civilians, according to the UN. The war has left Yemen fragmented and facing a humanitarian crisis.
  Meanwhile, IS and Al-Qaeda in the Arabian Peninsula (AQAP) have exploited the conflict to expand the territory under their control.
target: At least 22 people have been killed by three suicide bombings in checkpoints in the southern Yemeni city of Aden, officials say.