"Ammonnews was completely hacked and closed down. Only the Jordanian security services have the technical capacity to do this," chief editor Basel Okoor told AFP.
"We received today (a message) that said: 'You are working against the interests of the state, we are going to hack you', which was the case a few minutes later," Okoor said.
Calling up the Ammonnews home page on Monday produced this message in Arabic: "Ammon's management announces the site has been shut down by order of the security services."
Okoor said the personal email accounts of his staff had been hacked as well, and that they no longer had "technical access" to the site.
Ammon on Sunday said it had been the target of "piracy and anonymous attacks" for having published a statement by 36 prominent individuals from the major tribes in Jordan that are the backbone of the kingdom.
The statement -- issued against the backdrop of mass protests in Egypt -- spoke of a "crisis of authority" and "profound corruption" in Jordan, adding that the kingdom would "sooner or later" face a popular revolt.
Ammonnews was Jordan's first news site when it launched in 2006. Fifty others have since sprung up, but Ammonnews remains the most popular with 250,000 daily visitors, according to data from web traffic monitor Alexa.
Popular discontent in Jordan has manifested itself in several protest rallies against rising prices and corruption, although none have called for regime change.