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White House spokesman Jay Carney said Mr. Kerry’s comments don’t reflect any new information gleaned by authorities probing a Chechnya trip made last year by the elder brother.

“In a situation like this, we ought to let the investigators do their work and not jump to conclusions, as the president said on Friday,” Mr. Carney said.

Mr. Kerry weighed in on the emerging narrative behind the Boston Marathon bombers during a visit Wednesday to Brussels, where he told reporters, “We just had a young person who went to Russia, Chechnya, who blew people up in Boston.”

“He didn’t say where he went, but he learned something where he went, and he came back with a willingness to kill people,” Mr. Kerry said.

At the State Department on Wednesday afternoon, Patrick Ventrell, the department’s acting deputy spokesman, sought to clarify the remarks, saying his boss “was simply expressing broad concern about radicalism and not necessarily offering any more specific information about this case.”

FBI agents have begun to paint an alternative portrait during recent days, though 19-year-old Dzhokhar reportedly has admitted to investigators that he played a role in the bombings and that he and his 26-year-old brother held Islamist beliefs.

Federal investigators told Capitol Hill lawmakers on Tuesday that the brothers picked up their ideology and bomb-making skills online and did not appear to have connections to any larger terrorist groups.

Mr. Ruppersberger on Wednesday repeated reports that the brothers learned to make the pressure-cooker bombs that they used at the marathon from Inspire, the online al Qaeda magazine. He also said that investigators had revealed to lawmakers their belief that the device used to trigger the bombs was from child’s remote controlled car.

Russian’s RIA Novosti news agency reported that parents Anzor Tsarnaev and Zubeidat Tsarnaeva will come to the U.S. on Thursday. Family members have said they want to bury their elder son in Russia and have accused the U.S. of framing the pair.

Susan Crabtree contributed to this report.