U.S. authorities are still investigating whether the Thursday attack on a military recruiting center and a Navy support center is an act of domestic terrorism, but jihadist sympathizers on Twitter wasted little time declaring it one.

Over the last 48 hours, Twitter accounts aimed at recruiting extremists and supporting Islamic extremist terrorist attacks have hailed the alleged shooter a martyr and flooded the social media site with praise for the attack, which killed four U.S. Marines and one sailor.

While it is still unclear whether the alleged shooter, Mohammad Abdulazeez, was in contact with Islamic radicals overseas, dozens of Twitter accounts rushed to proclaim support for him, labeling him a "lion," and a courageous "mujahid," or holy warrior.

"May Allah accept the shahadah of our fervent brother Muhammad Yusuf Abdulazeez," one sympathizer tweeted. "The #Chattanooga Mujahid."

In Islam, the "Shahadah" refers to the "testimony" of its believers, or acts that bear witness to Allah being the one true god and to Muhammed as Allah's prophet.

Another tweet warned the hashtag #Killorbekilled and #Chattanooga and said "Actions breed retaliation nd (sic) we swear by Allah til death, we'll avenge all the Muslim blood spilt by the west."

Still another, tweeted: "He got shahadah:

1.) fight the worst kuffar on Earth – US Marines

2.) On Eid Day

3.) On a Friday

What a gud ending #ChattanoogaShooting."

Joyce Karam, the Washington bureau chief of Al-Hayat, a leading pan-Arab paper, tried to draw attention to a tweet in Arabic she found particularly offensive.

"This #ISIS support is quoting former AQ preacher Anwar Awlaki in praising #Chattanooga shooter. @twitter allows," she wrote Thursday night.

Counterterrorism groups have pointed to a late June call for attacks during Ramadan from the spokesman for the Islamic State, Muhammed al-Adnani on Twitter, as the latest example of how the Islamic State is weaponizing the popular social media site.

The Counter Extremism Project, a nonprofit formed to combat the threat from extremist ideologies, has an ongoing social media campaign using the hashtag #CEPDigitalDisruption to try to track, target and shut down hundreds of Twitter and Facebook accounts. It is currently monitoring the tweets praising the Thursday attack and trying to appeal to Twitter to take the most offensive or incendiary tweets down.

Last week FBI Director James Comey expressed alarm over the Islamic State and other extremists flood of recruiting messages on Twitter.

The Islamic State, Comey said, is a nimble, social-media savvy foe that uses Twitter as its go-to propaganda platform to incite jihad in Syria, Iraq, Africa, Europe and the United States.

"ISIL is totally different" than how other terrorist groups like al Qaeda have operated, he said, referring to another name for the Islamic State. "ISIL is reaching out primarily through Twitter to about 21,000-now English language followers."

"There's a group of tweeters in Syria, and their message is two pronged: Come to the so-called caliphate and live the life of some sort of glory or something, and if you can't come, kill somebody where you are. Kill somebody in uniform, kill anybody, if you can cut their head off, great. Videotape it. Do it, do it, do it," he said. "They're pushing this through Twitter."