Under the deal, Berlin pledged to respond to any attempt by Russia to wield energy as a weapon against Ukraine and other central and eastern European countries.
Officials say billions more will be needed to rebuild homes, businesses and roads as Berlin deals with one of the worst floods in decades.
Belgium's king and queen visited the flood-stricken town of Verviers to lead the nation in a minute of silence, while Germany said the number of people who lost their lives rose to 165, bringing the death toll in both countries to 200.
German Chancellor Angela Merkel says the world must step up efforts to tackle the climate crisis, as global warming makes extreme weather events more likely.
The real scale of the disaster is only now becoming clear, with damaged buildings being assessed and efforts under way to restore gas, electricity and telephone services.
Early observations suggest the rains might have been encouraged by a low-pressure system parked over western Europe for days, at it was blocked from moving on by high pressure to the east and north.
Search and rescue operations continue for hundreds more who are still unaccounted for or in danger as devastating floods hit western Germany and Belgium.
In a Twitter post, Robben said retirement is a difficult choice, and thanked everyone for their support.
Adding to the devastation, several more were feared dead in a landslide in northern Germany triggered by floods. Hundreds were unaccounted for in the country, while in Belgium more than 21,000 people left without electricity in one region.
Despite failing to resolve differences between Washington and Berlin, the US president said that he and the German chancellor are united in their conviction that "Russia must not be allowed to use energy as a weapon" against its neighbours.
Recent storms across parts of western Europe made rivers and reservoirs burst their banks, triggering flash floods and claiming 59 lives in Germany and killing 9 people in Belgium.
A study by Turkish experts revealed poor political participation of Muslims in the UK, France and Germany as a proportion of the population.
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