Governments working on the proposed new global deal on climate change, to be agreed this December, must step up their efforts after a slow week of talks produced little progress, observers have said.

In December, governments will meet in Paris to decide a new global agreement on greenhouse gas emissions, which would kick in from 2020 when current international commitments on emissions expire.

This week, officials have been meeting in Bonn to hammer out some of the final details of such a deal. However, progress has been slow and the talks – the final official negotiating days before Paris – ended without a clear conclusion.

The draft text of an agreement went from about 20 pages to more than 30 pages in the course of the week, despite French hopes that it could be slimmed down. Disagreements emerged over key issues such as the financial assistance from rich countries to poorer ones to help them cut emissions and cope with the effects of global warming.

Before Paris, ministers will meet again formally, and there will be informal discussions among countries to smooth out differences. There were no major catastrophes in Bonn – no countries walked out or publicly said they would not agree to a deal in Paris. Previous UN climate meetings have often been marred by such disagreements. For these reasons, the French hosts are still hopeful that an agreement will be reached in Paris, but the discussions must be stepped up and world leaders may need to intervene to ensure their negotiators are willing to forge a deal.

Jennifer Morgan, global director of the climate programme at the World Resources Institute, said: “Negotiators made some significant strides in Bonn but a much more vigorous pace is needed to secure a strong climate agreement in just a few weeks. We’ve been running a marathon for years to reach this point. Now we need an all-out sprint to get over the finish line in Paris.”

She said the draft text showed countries were close to reaching consensus on issues such as cutting greenhouse gas emissions, and the transparency needed for international monitoring of such efforts. However, she said, the issue of financial assistance to the poor was still showing “more fundamental differences”.

More than 150 countries have now submitted plans on limiting their greenhouse gas emissions beyond 2020, when current commitments expire. These commitments cover about 90% of the global economy, and if followed through should lead to global warming of no more than 2.7C, according to analysis, which still falls short of the 2C limit that scientists say gives the world an even chance of avoiding catastrophic and irreversible warming.

Martin Kaiser, of Greenpeace, called for countries to speed up the negotiating process. “This process is too important to be a high-risk poker game. They need to put down their cards and play together as a team.”

Recent analyses have shown that the financial assistance agreed for developing countries by 2020 is achievable. At the Copenhagen climate summit in 2009, at which the biggest developed and developing countries jointly agreed for the first time to limit their emissions by 2020, a package of financial assistance to be worth $100bn a year by 2020 for poor countries was agreed. Developing nations want it to be restated that they will receive this, as a precondition of any deal in Paris. The OECD has said that on current funding levels, that figure is likely to be met by the 2020 deadline.