The White House on Friday condemned twin suicide bombings on Yemeni mosques that killed at least 142 worshippers, but said it was too early to pin blame on the Islamic State group.
Describing the attacks in Sanaa as unprovoked, White House spokesperson Josh Earnest said there is not, as yet, a "clear operational" link between Yemeni extremists and the Islamic State in Syria and Iraq.
"The United States strongly condemns today's suicide bombings," Earnest said.
"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."
In an online statement, the previously unknown Sanaa branch of IS claimed responsibility for the bombings and said they were "just the tip of the iceberg."
The White House said: "We cannot at this point confirm the voracity of the claim." "We have seen these kinds of claims in the past from other extremist groups," Earnest said, adding that claims of allegiance to Islamic State are often made for propaganda purposes.