The White House on Friday condemned twin suicide bombings on Yemeni mosques that killed more than 120 worshipers.
Describing the attacks in Sanaa as unprovoked, White House spokesman Josh Earnest said there is not, as yet, a "clear operational" link between Yemeni extremists and Daesh terrorist group.
"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 Daesh 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.