Several mosques have been hit in a series of explosions in the Yemeni capital, Sanaa, causing dozens of casualties, officials say.
At least two blasts were caused by car bombs. Health and security officials said more than 20 people had died.
A building reportedly used as the headquarters of Houthi rebel officials was also hit.
The Islamic State (IS) militant group, which has carried out attacks in Sanaa before, said it was behind the blasts.
In a statement posted online, IS said that four car bombs targeted two areas of worship, as well as a house and an office belonging to what it called "Houthi apostates", referring to the Shia Houthi rebels.
In March, IS attacks on mosques used mainly by Houthis left more than 130 people dead.
Evening prayer attack
Pictures posted on Twitter showed flames leaping from the site of one of Wednesday's blasts, and residents said ambulances were rushing to the scene.
The bombs exploded as people arrived for evening prayers, witnesses said.
Attacks on a house belonging to one Houthi official and the workplace of another official were also reported.
Yemen has been in turmoil since Houthi rebels overran Sanaa last September, forcing the government of President Mansour Abdrabbuh Hadi to flee.
In late March, a coalition led by Saudi Arabia began targeting the rebels with air strikes. Since then, more than 2,000 people have been killed in the conflict, including at least 1,400 civilians, according to the UN.
It has warned of a "catastrophic" humanitarian situation, with an estimated 20 million Yemenis in need of aid.
UN-brokered talks are under way in Geneva, but there have been no reports of progress. Mediators had been hoping to broker a ceasefire during the holy month of Ramadan, which starts on Thursday.
On Wednesday, a senior representative for Mr Hadi who is currently in Geneva, Abdelaziz Jubari, said his house had been blown up by the Houthis.
The port of Aden has seen particularly fierce fighting between rebels and Hadi loyalists. Earlier on Wednesday, authorities said at least 31 people were killed when an air strike hit civilians fleeing from the southern city, the Associated Press reported.
The Houthis, who are from the Zaidi branch of Shia Islam, have also been battling militants from al-Qaeda in the Arabian Peninsula (AQAP).
AQAP executed two men it accused of spying for the US on Wednesday, tying their bodies to poles and hanging them from a bridge in the south-eastern city of Mukalla, residents said.
They said the men were accused of planting chips on AQAP leaders, allowing them to be located by US drones.
AQAP confirmed on Tuesday that its leader, Nasser al-Wuhayshi, had been killed in a drone strike.
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