In its English-language radio broadcast, the group praised the Wednesday shooting that killed 14 people and wounded 21 others.
"Two soldiers of the Khilafah (caliphate) executed an attack on the Inland Regional Centre in San Bernardino, California," the Islamic State radio broadcast said in English.
Islamic State refers to the swathe of territory it controls in Syria and Iraq as an Islamic caliphate.
The group's Arabic-language radio broadcast earlier in the day had referred to the attackers as "supporters of the Islamic State."
The English-language broadcast said the attackers, Syed Farook, 28, and his 29-year-old Pakistani wife Tashfeen Malik, were "killed in the path of Allah."
Female attacker from DG Khan praised Da’ish chief
But the group stopped short of issuing an official claim of responsibility for the shooting in the format it has used in the past for attacks in Paris and elsewhere.
The FBI said late Friday it was probing the attack as "an act of terrorism" after reports that Malik had pledged allegiance to IS on Facebook.
Package addressed to home of California shooters deemed safe: police
A package addressed to the Southern California home of the couple was inspected on Friday and determined to pose no threat, the local police chief said on Twitter.
San Bernardino shootings: Pakistani-origin couple behind California carnage
A United Parcel Service driver noticed the package was addressed to the couple's Redlands home and as a precaution the driver returned to a UPS facility, San Bernardino Police Chief Jarrod Burguan said on Twitter.
Police were notified and arrangements were made to have a bomb squad unit inspect the parcel, Burguan said, later adding in a follow-up post, "item was safe, posed no threat."
The Redlands couple, Syed Rizwan Farook, 28, and Tashfeen Malik, 29, shot to death 14 people at a county government holiday party in nearby San Bernardino on Wednesday and died hours later in a shootout with police.
Pakistani-origin couple kept tight lid on plans for San Bernardino shooting
The FBI has said it is investigating the attack as an "act of terrorism."
The couple had amassed a dozen pipe bombs at their Redlands townhouse and police also found bomb-making equipment there, authorities have previously said. Burguan in his posts on Twitter did not indicate what the package contained or how long ago it was ordered.
The parcel came from a reputable vendor, he said. A San Bernardino police supervisor was not available for additional comment early on Saturday.
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