French political leaders from left and right were left unconvinced Thursday by marathon talks aimed at finding common ground with President Emmanuel Macron, who is struggling to build new momentum in a hung parliament.

People close to the centrist leader said he would "send a letter summarising the talks and the suggested work areas, that anyone can amend" before a new round of discussion.

But conservative leader Eric Ciotti, Macron's most obvious potential ally, told broadcaster France 2 hours after the 12-hour talks broke up at 3:00 am (0100 GMT) that he was "unconvinced for now".

"I don't know where any of this will go," he added, while calling the all-party talks "timely".

There were harsher words from Manuel Bompard, coordinator of hard-left France Unbowed, who told France Info it had been "grotesque" to "spend 12 hours to get no serious answers, no measures, no concrete announcement, when we know what difficulties the country faces today".

"We came, we saw and we were disappointed," added Greens chief Marine Tondelier, another member of the NUPES left-wing alliance.

Close Macron ally Francois Bayrou told broadcaster LCI later Thursday that leaders had agreed to hold a "major conference on our institutions".

They would discuss topics including referendums and proportional representation in parliament, he added.

Referendum risk

With referendums in the air, the left is hoping for a public vote to reverse this year's unpopular pension reform while the conservatives and far right both want one on immigration.

People in Macron's camp -- aware referendums have often backfired on French presidents in the past -- have floated an alternative, a series of multiple-choice questions dubbed a "preferendum".

"By asking several questions, people may vent on one of them and respond on the issues on all the others," government spokesman Olivier Veran told broadcaster BFMTV on Monday.

Constitutional experts have raised doubts on whether such a ballot would be legal and what standing it would have if it went ahead.

Bayrou told LCI that Macron "said it wasn't his idea, that he didn't know what it is, but that we'll look more closely at it".

Citing other participants, daily Le Monde reported that Macron "openly laughed at the idea".

Olive branch 

Re-elected last year against far-right chief Marine Le Pen, Macron lost his majority in the lower house in subsequent parliamentary elections.

Until now his government has made bill-by-bill alliances to get laws passed, or relied on an unpopular provision allowing them to be rammed through on the back of a confidence vote.

The fierce rejection of his pensions reform earlier this year, a week of spectacular riots in June-July and his failure to reach a deal with the right on changes to immigration law all suggest the method has reached its limits.

People in his entourage insisted to AFP that Wednesday night had been "a great political moment, a great moment of unity, of recognition and responsibility", saying Macron's choice to extend an olive branch to the opposition had been "fruitful".