There are reports of up to 142 people having been killed in twin suicide bombings at mosques in Yemen's capital Sanaa on Friday. An unverified claim of responsibility has been made by extremist group Islamic State.
Authorities say at least 100 people were wounded in the blasts, when four bombers detonated their explosive belts during busy Friday prayers.
Reports on how many have been killed vary, with numbers ranging from 77 to as high as 142.
Rebel-owned broadcaster Al-Masirah also reported a fifth attack in the southern city of Sadaa was foiled when the bomb went off early, killing just the bomber.
The mosques were known to be frequented by supporters of the Houthis, who control most of the country's north, although Sunni worshippers also visit the sites.
It's Yemen's deadliest militant attack since Houthi rebels seized the capital six months ago.
Survivors likened the explosions to an earthquake, with pictures broadcast by Al-Masirah showing people rushing out of the mosque carrying bodies.
Some supporters of the militant group "Islamic State" (IS) have claimed responsibility for the attacks, posting a statement on Twitter warning of more to come.
The group is a sworn enemy of the extremist al Qaeda organization.
If proven, it would be the group's first sectarian attack.
It comes after the organization claimed it was behind a deadly attack on a museum in Tunisia on Wednesday, in which 21 people were killed.
In the US, White House spokesman Josh Earnest condemned the bombings:
"We deplore the brutality of the terrorists who perpetrated today's unprovoked attack on Yemeni citizens, who were peacefully engaged in Friday prayers."
But he cautioned against attributing the attacks to IS, saying these claims are sometimes made for propaganda purposes.
Meanwhile, unidentified warplanes dropped bombs near the presidential palace in the southern city of Aden for the second day.
Officials say President Abed Rabbo Mansour Hadi was unhurt, with anti-aircraft guns returning fire.
Sunni-backed Hadi is involved in a power struggle with Houthi rebels, allegedly supported by Iran and Yemen's ousted former president Ali Abdullah Saleh.
Hadi fled to Aden in February, after being held under house arrest for a month in Sanaa by Houthi forces.
He maintains he is still leading the troubled Arab state.
On Thursday Aden's airport was forced to close after fighting between rebels and Hadi loyalists left 13 dead.
In the wake of the Houthi takeover of Sanaa some Western nations closed their embassies, while other Gulf nations moved operations to Aden.
an/sb (AFP, AP, Reuters)