Citing heavy losses in previous years, Nepszabadsag's owner Mediaworks said yesterday that halting the left-leaning paper's online and print operations was done purely for commercial reasons.
Journalists at the paper said they had been given no advance notice and were suddenly prevented from entering the workplace.
Talks between Mediaworks management and senior editors today failed to reach agreement on publishing the paper's Monday edition or restarting its online version, editor-in-chief Andras Muranyi said.
Regardless of who the new owner is, Nepszabadsag "should remain independent" he said.
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Opposition parties, activists and several staff blamed the abrupt suspension on Prime Minister Viktor's Orban's ruling right-wing party Fidesz cutting off oxygen for media that do not toe the government line.
Critics said the timing of the move was suspicious, coming days after Nepszabadsag made corruption allegations against two close allies of Orban.
"The sudden closure of Nepszabadsag sets a worrying precedent," European Parliament president Martin Schulz said in a tweet.
Fidesz in a statement called Austrian-owned Mediaworks' move a "rational economic decision", but Muranyi said that "rather than a financial one, the publisher has made some other kind of decision in this case".
Earlier today, Nepszabadsag staff tried to enter the building, but found the doors locked and the windows blacked out.
Around 100 people gathered outside the building to show support for the journalists.
Since taking power in 2010, Orban has often been accused of trying to silence critical voices in the press, including turning public media channels into government mouthpieces, and enabling allies to buy private media organs.