Soon after the deadly shooting in California, a flurry of tweets by supporters of Islamic State boasted of the terror group's connections to the attack in which 14 people were killed and 21 others injured.
In a report, the Investigative Project on Terrorism (IPT), a US-based non-governmental body that investigates into terror incidents, said that a mid-level IS commander, who variously refers to himself as Jazrawi_DAESH tweeted that the Pakistani-origin couple who carried out the attack were "special agents of IS" and that they murdered the innocents in "response to so called US bombing of Muslims".
The IPT said that the mass shooting occurred on the same day an Islamic State propaganda video vowed attacks against Washington and New York.
"#BringItOn CHALLENGE ACCEPTED !!# AMERICAONFIRE WHEN WE SAY WE'LL KILL YOU IN UR COUNTRIES WE MEAN IT (sic)," IS supporter Alharthidz Jarallah tweeted on the day of the attack.
According to IPT, he later tweeted that IS "warned USA led coalition and they don't listening (sic)".
In another tweet, Jarallah taunted the US, saying: "That's what you get America don't play with us cuz you'll get burned #AmericaBurning."
Another IS supporter, @Pashbakr1, tweeted wondering if the killers were lone jihadists, "Lone Wolf Blessed Attacks !?"
IPT further said that a leading IS propagandist who tweets under the handle 'Muslimah' congratulated the couple for the San Bernardino assault, calling them "martyrs".
"May Allah Accept Our Brother & Sister who were martyred after carrying out an operation against Crusaders in USA," she tweeted.
US investigators yesterday said that the Pakistani wife of the Pakistani-American man who together carried out the deadly shooting, had pledged allegiance to IS leader Abu Bakr al-Baghdadi on Facebook.
While the woman, Tashfeen Malik, a mother of six-month old baby, was a Pakistani national her husband Syed Farook's parents migrated to the US from Pakistan.
Both were killed on the day of shooting during an exchange of fire with police.
The FBI is investigatiing the shooting as an act of terrorism.