BERLIN -- Chancellor Angela Merkel pressed ahead with efforts to form a new German government on Friday after a night of negotiations failed to resolve differences between the four parties involved. Participants suggested that they may need several more days.

Germany's Sept. 24 election left Merkel's two-party conservative bloc seeking a previously untried coalition with the pro-business Free Democrats and the traditionally left-leaning Greens. After four weeks of exploratory talks, their immediate aim now is to establish enough common ground to embark on formal coalition negotiations.

The parties aimed to wrap up the talks Thursday night but, after haggling for about 15 hours, adjourned until Friday.

So far, they have struggled to overcome major longstanding differences on immigration and climate change-related issues, but also on financial questions. A dispute over whether migrants granted protection that falls short of asylum should be allowed to bring close relatives to Germany is proving particularly thorny.

"It's not easy -- we saw that yesterday," Merkel said Friday. "Tying the ends together is not exactly trivial but, despite all the difficulties, I am going into these negotiations with the will to fulfil the task voters gave us of forming a government."

Failure could lead to new elections as the centre-left Social Democrats, Merkel's partners in the outgoing government, are adamant they will go into opposition after a disastrous result in September. Polls so far suggest that a new vote would produce a very similar parliament to the current one, making efforts to form a new government similarly difficult.

A decision to open coalition negotiations, which would likely last several more weeks, would require approval by a Greens party congress later this month.

The Free Democrats' leader, Christian Lindner, said the parties agreed they should "use the coming days" to overcome their differences.

"We will use this weekend to achieve a good solution," Merkel's chief of staff, Peter Altmaier, told ARD television. He wouldn't specify when exactly the talks might conclude.

The Social Democrats' leader, Martin Schulz, indicated that his party has no intention of budging from its refusal to consider entering Merkel's fourth-term government. He said that the outgoing government lost a cumulative 14 per cent of the vote in September and was voted out.

Schulz argued that the parties now negotiating received a mandate from voters to form a government, and if they can't agree a deal "this mandate must be given back to those who decide -- namely, the voters."