At least 142 people have been killed and hundreds more injured after four suicide bombers attacked two mosques in the Yemeni capital Sanaa.
The bombers struck during Friday prayers at mosques mainly used by supporters of the Shia Muslim Houthi group which recently seized control of the government.
The attackers detonated their explosive belts inside and outside the buildings.
One witness said: "A man with a crutch and his leg covered with plaster showing the Houthi sign on the crutch entered the inside of the mosque, then we heard the explosion."
A spokesman for the country's health ministry said at least 30 of those wounded in the attacks were in a critical condition in intensive care.
In an online statement, the previously unknown Sanaa branch of Islamic State claimed responsibility for the bombings and said they were "just the tip of the iceberg".
The US condemned the attacks, but said it was too early to confirm whether IS was involved.
White House spokesman Josh Earnest said there is not, as yet, a "clear operational" link between Yemeni extremists and IS fighters in Syria and Iraq.
"We express our condolences to the families of the victims, we deplore the brutality of the terrorists who perpetrated today's unprovoked attack on Yemeni citizens, who were peacefully engaged in Friday prayers," he said.
Yemen is divided by a power struggle between the Iranian-backed Houthi rebels in the north and UN-recognised President Abd-Rabbu Mansour Hadi, who fled to the southern city of Aden in February after escaping house arrest in the capital.
He has established a rival seat in Aden with the backing of Sunni-led Gulf Arab states but twice in the last two days unidentified aircraft have attacked his presidential palace.
A government spokesman said the President was not in the palace at the time and is unharmed.
