Millions of users were affected, and thousands took to Twitter on Wednesday and Thursday to complain under the hashtag #facebookdown.
A spokesman for the social network said the company was cooperating with investigators in multiple federal probes, without addressing the grand jury inquiry specifically.
"We're focused on working to resolve the issue as soon as possible, but can confirm that the issue is not related to a DDoS attack", Facebook said.
Facebook acknowledged the outage on Wednesday while saying it did not appear to be the result of a denial-of-service attack.
Chief product officer Chris Cox announced his resignation, becoming the highest-ranking manager to depart amid the turmoil at the leading social network.
Facebook temporarily removes Elizabeth Warren's ads calling for breakup of Facebook
Facebook removed those ads, citing their violation of the company's policy of not allowing ads which use the Facebook brand. The legislation would result in, for example, Google's "Search" and Amazon's "Marketplace" being forced to spin off.
Erdan: 'We will not allow a religious war caused on Temple Mount'
A fire rages in a police post on Jerusalem's Temple Mount after a Molotov cocktail was thrown at it on March 12, 2019. However, in February Palestinians opened the areas, breaking Israeli locks on an outer metal door that leads to them.
Google just released the first Android Q beta
There are many other features part of Android Q beta 1 and possibly more will be added in the future beta version of the platform. While there aren't any major consumer facing features yet, there are a few things of note, primarily with a focus on privacy.
Instead of selfies and status updates, many Facebook users got an error message during the outage that said: "Sorry, Something went wrong". Will Cathcart will be the new head of WhatsApp.
Shares declined 1.8 percent in NY, and have jumped 32 percent this year through Wednesday's close.
FILE PHOTO: Silhouettes of mobile users are seen next to a screen projection of Facebook logo in this picture illustration taken March 28, 2018.
The news comes with regulators, investigators and elected officials in the USA and elsewhere in the world digging into the data sharing practices of Facebook. Back in November past year, the social media platform also suffered from issues as well.
The New York Times recently reported that Facebook is putting a ton of resources into its own blockchain-fuelled payment system that could help it mitigate its reliance on advertising as its dominant source of revenue.
"It has already been reported that there are ongoing federal investigations, including by the Department of Justice", a Facebook spokesperson told AFP.