Louvre suspect may have tweeted about IS before attack
The tweets came from "a Twitter account whose owner could be the attacker", the source said, adding that investigators were unable to formally confirm this at the moment.
The messages were posted in Arabic on the account of Abdallah El-Hamahmy.
"In the name of Allah... for our brothers in Syria and fighters across the world," he wrote at 9.31am (0831 GMT).
One minute later he posted another tweet, making reference to the extremist group.
At least ten tweets were posted between 9.27 am and 9.34am, shortly before the attack began at the Louvre at 9.50am.
El-Hamahmy, whose account was still publicly accessible early on Saturday, tweeted on January 26 about travelling from Dubai to Paris, a journey which corresponds to the movements of the alleged attacker.
Investigators are also examining an iPhone 7 and iPad belonging to the assailant, whose identity had yet to be confirmed late on Friday.
However French investigators believe the man, who was shot and wounded by a soldier following the attack, is a 29-year-old Egyptian who entered the country on a tourist visa a week earlier.
Prosecutor Francois Molins reported on Friday night that his condition was stable.
The Louvre, which is home to numerous celebrated art works, including the Mona Lisa, is due to reopen on Saturday.
The incident has thrust security and the terror threat back into the limelight three months before elections in France, with authorities saying it was a "terrorist" assault.
France is the second contributor to the US-led coalition that has carried out thousands of airstrikes against IS in Iraq and Syria and provided military equipment, training and advice to Iraqi forces.
President Francois Hollande last month said fighting IS was key to preventing attacks at home.