Suicide bombers have attacked two mosques in Yemen’s capital, Sanaa, killing at least 77 people and wounding 121 others, medics say.
Worshippers were attending noon prayers at the Badr and al-Hashoosh mosques when at least three attackers struck.
The mosques are used mainly by supporters of the Zaidi Shia-led Houthi rebel movement, which controls Sanaa.
Islamic State (IS), which set up a branch in Yemen in November, said it was behind the attacks.
If confirmed, the attacks would be the first carried out by IS in Yemen.
There are also severe tensions between the Houthi rebels and various powerful, armed elements in Yemen, including militants from al-Qaeda.
Witnesses said at least two suicide bombers attacked the Badr mosque, in the south of Sanaa.
One entered the building and detonated his explosive device among dozens of worshippers, the witnesses added. Survivors then sought to escape through the main gates, where the second bomber was waiting.
Jazeera reported that the prominent Houthi cleric al-Murtada bin Zayd al-Mahatwari, the imam of the Badr mosque, was among those killed.
A man who was at the al-Hashoosh mosque, in a northern district of the capital, said he was thrown about 2m (6ft) by the blast.
“The heads, legs and arms of the dead people were scattered on the floor of the mosque,” Mohammed al-Ansi told Associated Press news agency, adding that “blood is running like a river”.
Mr Ansi said that many of those who were not killed by the explosion were seriously injured by shattered glass that fell from the mosque’s windows.
The rebel-run al-Masirah TV channel broadcast footage from inside the al-Hashoosh mosque showing volunteers using bloodied blankets to carry away victims. Bodies were also lined up in the prayer hall.
Al-Masirah reported that hospitals in the city had made urgent appeals for blood donations to help treat the large number of casualties.
Yemen is the base of al-Qaeda in the Arabian Peninsula (AQAP), a powerful offshoot of the jihadist militant group that has carried out similar suicide attacks on Houthi supporters.
However, IS is also gaining ground in the country.
The bombings come a day after deadly clashes in the southern city of Aden, between forces loyal to President Abdrabbuh Mansour Hadi and those supporting his predecessor, Ali Abdullah Saleh.
Warplanes later targeted the presidential palace in Aden, where Mr Hadi has been based since fleeing Sanaa last month after the rebels placed him under effective house arrest.
The president, who aides said was evacuated to a “safe place” after the air raid, described Thursday’s events in Aden as a “failed military coup against constitutional legitimacy”.
Mr Saleh was forced to hand over power to Mr Hadi in 2011 after mass protests, but has remained a power-broker. He is currently allied with the Houthis, against whom he fought wars when he was president.