Cross-party talks on the Leveson press reforms have broken down, the prime minister has confirmed.
David Cameron told Nick Clegg and Ed Miliband the gap between them was "too great" to bridge, the BBC understands.
He said he would publish plans for a royal charter to establish a tougher press regulator on Monday and urged them to support the proposals.
Labour said he was making an "historic mistake". The Lib Dems said the situation was "extremely regrettable".
Campaign group Hacked Off said the prime minister's announcement "shows that he's still protecting his friends in the press and betraying press abuse victims".
MPs are expected to debate the Conservative proposals on Monday.
Mr Cameron said a royal charter would help to create the world's "toughest" regulatory system.
The proposals would see a new independent body oversee the system of press self-regulation.
Lord Justice Leveson's report, which was published in November, called for a new independent press watchdog underpinned by legislation - something the Lib Dems and Labour support.
The 2,000-page report into press ethics found press behaviour was "outrageous" and "wreaked havoc with the lives of innocent people".
'Very disappointed'
Speaking at a Number 10 press conference, Mr Cameron confirmed cross-party talks on press reform had "concluded without agreement".
He said press treatment of those including the families of missing girl Madeleine McCann and murdered teenager Milly Dowler was "absolutely despicable", stressing he wanted a new system to prevent such things happening.
But he insisted a full legislative response presented "real dangers".
"It crosses the Rubicon in terms of endangering press freedoms," he said.
He added a royal charter approach was a "proven way of establishing a public body without the need for legislation".
The prime minister emphasised a charter would ensure "the independent self-regulation that Lord Justice Leveson recommended while simultaneously protecting the precious independence and freedom of our press".
He said he was putting forward the most "workable" and most "deliverable" plan he could.
"The route I have set out is the fastest possible way to deliver the strong self-regulation body that Leveson proposed - that can put in place million-pound fines, prominent apologises and get justice for victims in this country.
'Nothing agreed'
"The deal is there to be done, it is the fastest way to get proper justice for victims."
Mr Cameron also said other parties could table their own proposals: "They can back my amendments or they can grandstand and end up with a system that I don't believe will work."
"If you establish a system that people don't take part in you haven't solved the problem."
The prime minister's comments come after the three main political parties held face-to-face talks on Wednesday to discuss whether plans for a new watchdog should be underpinned by legislation.
But Mr Cameron told Lib Dem leader Mr Clegg and Labour leader Mr Miliband by phone on Thursday he would not accept a press law of any kind, the BBC's political editor Nick Robinson said.
He said he feared it would be open to constant amendment in parliament, producing a system of regulation way beyond that which Lord Justice Leveson recommended, added our political editor.
But Mr Miliband said Mr Cameron was "making an historic mistake".
The Labour leader said the prime minister's solution did not serve the victims of press intrusion as "ministers could change his proposals without reference to Parliament, and it's not properly independent of the press".
He added a cross-party solution could still be reached, even if Labour and the Lib Dems went above Mr Cameron's head to talk to Tory MPs.
Deputy Liberal Democrat leader Simon Hughes said Mr Cameron's move was "extremely regrettable", adding his party would not support a "simple charter".
He also called for sufficient time to debate other amendments "because some of us are determined to get it right and not to dishonour our pledge made after the Leveson report".
Media reform campaigner Max Mosley told the BBC passing a royal charter could put press regulation back to square one.
"The reason we need legislation is that whatever we agree, the press could not backslide on it," he said.
BBC political correspondent Norman Smith said there would now be "a showdown over Leveson - a Commons confrontation" between the Conservatives against the Lib Dems and Labour.
Mr Cameron knew they were considering having a vote and possibly wanted to be go on the offensive and force one, our correspondent said.
He also said that if the prime minister were to lose a vote he could at least turn to the press and say that he fought for their cause.