"Al Jazeera Media Network under cyber attack on all systems, websites & social media platforms," it said on Twitter.
The attack was also confirmed by a source at Al-Jazeera, who said the broadcaster was attempting to repel the hack.
"An attempt has been made, and we are trying to battle it," said the source.
Following the initial reports of a cyber attack, some viewers in the region said they could no longer receive Al-Jazeera television.
Al-Jazeera, one of the largest news organisations in the world, has long been a source of conflict between Qatar and its neighbours, who accuse the broadcaster of bias and fomenting trouble in the region.
The alleged cyber attack comes during a time of heightened tensions in the Gulf, which has seen Saudi Arabia, the United Arab Emirates, Egypt, Bahrain and other allies cut ties with Qatar.
Long-running tensions broke out into the open last month after Qatar claimed its state news site was hacked by unknown parties who posted "false" statements attributed to the emir in which he speaks favourably of Iran and the Palestinian Islamist group Hamas.
The remarks were widely reported as true across the region.
Earlier this month, Qatar said the FBI was helping it investigate the source of the alleged hacking.
Subsequently there were a media report suggesting that Qatar had been targeted by Russian hackers -- a claim dismissed by Moscow.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)