Wales Labour leader Rhodri Morgan says he has been given authority to talk to Lib Dem and Plaid Cymru leaders to try to "provide good governance for Wales".
Mr Morgan described the meeting as a "marathon session"
Labour AMs met on Tuesday to consider how to form an assembly government, after failing to win a majority in the Welsh assembly election.
Mr Morgan said he had a mandate to "start talks about talks" and "negotiations about negotiations".
But most Labour AMs prefer a deal with the Lib Dems, BBC Wales understands.
Labour is the largest party in the assembly after winning 26 of the 60 assembly seats.
Mr Morgan described the meeting in Cardiff Bay as a "marathon session" and said the whole group recognised that "we are not entirely masters of our own destiny now".
He said: "It is very early days and clearly I will have to keep the group and the wider party in Wales informed, as I'm sure the other party leaders involved in these negotiations will want to be doing with their groups and their wider parties as well.
"I will be seeking to have talks with Mike German and with Ieuan Wyn Jones so that we can see whether we can produce a sustainable government and a government which can deliver for the people of Wales over the next four years."
But BBC Wales understands that the majority of the Labour group regards the prospect of a deal with the Liberal Democrats as the "least worst option".
A possible coalition with the Liberal Democrats has already brought some criticism from within both parties.
Former AM Tom Middlehurst, who resigned from the Labour cabinet in 2000 over the Labour-Lib Dem coalition, said "hot money" was on a deal with the Liberal Democrats.
He also said a more informal arrangement with Plaid was possible, although he said this was less likely.
Labour polled five seats short of an overall majority
Mr Middlehurst said: "The price we had to pay for their (Lib Dem) co-operation was huge and out of all proportion to their electoral success in the assembly and that's the situation today - they're a political rump of just six seats and in some disarray themselves."
Merthyr Tydfil and Rhymney AM Huw Lewis said Labour faced some "unappealing prospects," adding he personally would not want to work alongside a Plaid Cymru minister.
"What was the message the electorate sent us? I think they clearly said 'we want Labour to govern,' but there was also an enormous 'but...' hanging over it," he said.
Welsh Liberal Democrat leader Lembit Opik MP said the three choices for his party seemed to be formal coalition, a "non aggression" pact or being in opposition.
But he said discussions were "at a very early stage".
"It's not the process that interests me, it's the outcomes," said the Montgomeryshire MP.
"For example in north and mid Wales, a lot of people feel excluded by the assembly and one question we'll make sure is asked is what's there for people in mid and north Wales."
Plaid Cymru AM Dafydd Elis Thomas said one option would be for Labour to "go it alone" and look for support on specific measures and policies.
Lord Elis Thomas, who has been presiding officer since 1999, said it could be good for the assembly as an institution and "keep it alive and lively".
Another Plaid AM Dr Dai Lloyd said there had been "no negotiations with Rhodri Morgan whatsoever".
He said: "There is no appetite for coalition whatsoever and we're now deeply entrenched as being the major opposition party, having made a significant advance and we've spent the weekend in a jubilant mood".
Conservative assembly leader Nick Bourne is understood to have contacted his group of AMs by phone.
Dr Jonathan Bradbury, a lecturer in politics at the University of Wales Swansea, said that mathematics after the election meant a Lab-Lib coalition gave "a stable basis for party government for the next four years". "When all the parlour game discussions are stripped away there are the two parties which can form a natural agreement," said Dr Bradbury.
"The context is different now. Back in 2000 there was a long period leading to an agreement.
"Now you have the experience of that partnership government and clearly there are views within the Lib Dem and Labour parties which don't exactly want a repeat of that experience and so the odds are on a more informal kind of agreement.
"Also within the Lib Dems there are electoral ambitions in Newport and Swansea - two of the 11 Labour marginals are here - and they want some freedom to compete in elections in the coming years."