The German Chancellor, 62, told a party rally in Munich: "The times in which we could completely depend on others are on the way out. I've experienced that in the last few days.
"We Europeans truly have to take our fate into our own hands.”
Angela Merkel added: “We have to fight for our destiny,” saying that both Germany and Europe would aim to keep on good terms with both Britain and the US.
Angela Merkel was speaking at a CSU conference
But in a rebuke to both the UK and Britain Mrs Merkel emphasised the need for warm relations between Berlin and the new French President Emmanuel Macron.
The Chancellor has just returned to to Germany from a G7 summit in Sicily which concluded without the countries agreeing a deal between the US and the other six major advanced countries on the 2015 Paris climate accords.
Merkel meets Trump at the White House
Fri, March 17, 2017
U.S. President Donald Trump has welcomed German Chancellor Angela Merkel to the White House in Washington DC
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U.S. President Trump and German Chancellor Merkel hold a joint news conference in Washington
The times in which we could completely depend on others are on the way out. I've experienced that in the last few days.
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German Chancellor Angela Merkel
Referring to the talks, she labelled the outcome of the "six against one" discussion "very difficult, not to say very unsatisfactory".
She told reporters: "The entire discussion about climate was very difficult, if not to say very dissatisfying.
"There are no indications whether the United States will stay in the Paris Agreement or not."
Angela Merkel (L) with Melania (C) and Donald Trump
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US President Donald Trump though took a much more positive line, writing on Twitter: "Just returned from Europe. Trip was a great success for America. Hard work but big results!"
Mr Trump had earlier tweeted that he would reveal whether or not the US would stick to the global emissions deal – which he pledged to jettison on the campaign trail – only next week.
Mr Trump has reportedly told "confidants," including the head of the Environmental Protection Agency Scott Pruitt, he plans to leave the international agreement on climate change, the Axios news outlet reported, citing three sources with direct knowledge.
Angela Merkel (L) and US President Donald Trump
He also reportedly described German trade practices as "bad, very bad," in Brussels talks last week, complaining that Europe's largest economy sells too many cars to the US.
Sunday's event saw Mrs Merkel renew bonds with the Christian Social Union (CSU), Bavarian sister party to her own centre-right Christian Democratic Union (CDU), ahead of a parliamentary vote in September.
Polls show the chancellor, in power since 2005, on course to be re-elected for a fourth term.
Angela Merkel (L) in discussions with Donald Trump
The latest poll by Emnid published today in Bild show support for Merkel’s bloc unchanged at 38 per cent, while the Social Democrats (SPD) support dropped one percentage point to 25 per cent.