Angela Merkel and her finance minister, Wolfgang Schäuble, have come under sharp attack at home for their handling of the Greek crisis talks, with some opposition politicians accusing them of blackmailing Athens.

Ahead of a special session of the Bundestag on Friday at which Merkel, the German chancellor, will ask parliamentarians to support negotiations for a third bailout for Greece, some MPs accused her and Schäuble of deliberately trying to split Europe.

Gerhard Schick, the financial expert of the Green party, accused the finance minister of acting “extremely dangerously” concerning his proposals for a temporary exit of Greece from the eurozone. “With his Grexit plan Schäuble was calling for the division of Europe,” he said. He called Schäuble’s plan “a completely new negotiating position”, which had been tabled without the approval of the rest of the German government.

The deputy leader of the far-left Linke, Dietmar Bartsch, meanwhile accused the German government of extortion. “This negotiation result is a German diktat and nothing other than blackmail,” he told German television.

Schäuble in particular had “smashed an awful lot of porcelain” during the talks, he added. With his Grexit paper he had “taken the axe to Europe. It is terrible what he did and the way he used it to threaten other countries,” Bartsch said.

Christian Lindner, the head of the liberal FDP party accused Merkel of adopting a “nebulous” negotiating strategy. He said her and Schäuble’s “change of direction” was “politically breathtaking and from a legal perspective extremely questionable”.

Opinion polls conducted shortly after the deal was struck on Monday morning, however, showed that the majority of German voters approved of the way in which the duo had managed the talks. According to a survey by ARD Deutschlandtrend, published on Monday evening, 64% of Germans applauded Schäuble’s behaviour, with 62% giving Merkel their backing.

#BoycottGermany - they owe the Greeks billions - always remember the facts over the pro EU fiction pic.twitter.com/EIwn6U4e82 — Tim-A-Roberts (@Tim_A_Roberts) July 13, 2015

Germans have been horrified and puzzled by the huge backlash against Germany on social media and throughout the European and US press.

“On the internet, Germany is the bogeyman,” said Bild in an article that analysed the flood of negative publicity. It also voiced alarm that on top of the #ThisIsACoup hashtag on Twitter, there was a growing movement calling for the boycotting of German products, under #BoycottGermany and #StopBuyingGermany.

While Merkel and Schäuble might have popular support, only 18% of Germans said they trusted Greece to implement the reforms it signed up to, with 78% saying they had no trust in the government of Alexis Tsipras.

The Sächische Zeitung in Dresden said that while it was to be welcomed that Greece would not be leaving the eurozone, there was no reason to consider the summit a success. “Whether the eurozone and the EU can really end the crisis is nothing more than a vague hope. No one can guarantee that the investment programmes will have the desired effect on the Greek economy and the overdue modernisation of its clapped-out political system,” it wrote in an editorial.